rustbuild: Quickly `dist` cross-host compilers
This commit optimizes the compile time for creating tarballs of cross-host
compilers and as a proof of concept adds two to the standard Travis matrix. Much
of this commit is further refactoring and refining of the `step.rs` definitions
along with the interpretation of `--target` and `--host` flags. This has gotten
confusing enough that I've also added a small test suite to
`src/bootstrap/step.rs` to ensure what we're doing works and doesn't regress.
After this commit when you execute:
./x.py dist --host $MY_HOST --target $MY_HOST
the build system will compile two compilers. The first is for the build platform
and the second is for the host platform. This second compiler is then packaged
up and placed into `build/dist` and is ready to go. With a fully cached LLVM and
docker image I was able to create a cross-host compiler in around 20 minutes
locally.
Eventually we plan to add a whole litany of cross-host entries to the Travis
matrix, but for now we're just adding a few before we eat up all the extra
capacity.
cc #38531
This commit optimizes the compile time for creating tarballs of cross-host
compilers and as a proof of concept adds two to the standard Travis matrix. Much
of this commit is further refactoring and refining of the `step.rs` definitions
along with the interpretation of `--target` and `--host` flags. This has gotten
confusing enough that I've also added a small test suite to
`src/bootstrap/step.rs` to ensure what we're doing works and doesn't regress.
After this commit when you execute:
./x.py dist --host $MY_HOST --target $MY_HOST
the build system will compile two compilers. The first is for the build platform
and the second is for the host platform. This second compiler is then packaged
up and placed into `build/dist` and is ready to go. With a fully cached LLVM and
docker image I was able to create a cross-host compiler in around 20 minutes
locally.
Eventually we plan to add a whole litany of cross-host entries to the Travis
matrix, but for now we're just adding a few before we eat up all the extra
capacity.
cc #38531
Recent versions of Cargo lift less output up into the "main" directory, so let's
look more inside the `deps` folder for changes to propagate differences.
Closes#38744Closes#38746
Despite what the comment says, we actually need to do this. We're not cleaning
out the stage0 compiler's sysroot, but rather just our own sysroot that we
assembled previously.
Gate on distcheck on Travis
This commit adds a new entry to the Travis matrix to gate on distcheck, the illustrious test process that has historically taken *8 hours* to complete and also breaks all the time on nightly. By adding it to Travis we should hope to never see nightly breakage (like https://github.com/rust-lang/rust/issues/38690) because of this ever again!
"But wait, surely we can't wait 8 hours for all PRs!" you might be thinking, and you are indeed correct. The distcheck added here is much more optimized for speed than the old buildbot instances for a number of reasons:
* We're not building *two host compilers* beforehand. The current distcheck bot does a cross for i686 Linux and x86_64 Linux before it actually runs distcheck, building 6 compilers and LLVM twice. None of this is done in parallel as well (e.g. `-j1`). Not doing any of this work will be a huge win!
* We're using sccache to compile LLVM, so it should be much faster. Distcheck on the bots didn't cache LLVM well and rebuilt it every time.
All in all, this version of "distcheck" should be exactly like other matrix entries that run tests except that it's a *little* slower to start as it has to create the source tarball then rebuild the build system in the distcheck dir. Overall this should be well under the 2 hours that Android is currently taking anyway.
Closes https://github.com/rust-lang/rust/issues/38691
rustbuild: Compile all support tools in stage0
This commit changes all tools and such to get compiled in stage0, not in
later stages. The purpose of this commit is to cut down dependencies on later
stages for future modifications to the build system. Notably we're going to be
adding builders that produce a full suite of cross-compiled artifacts for a
particular host, and that shouldn't compile the `x86_64-unknown-linux-gnu`
compiler more than once. Currently dependencies on, for example, the error index
end up compiling the `x86_64-unknown-linux-gnu` compiler more than necessary.
As a result here we move many dependencies on these tools to being produced by a
stage0 compiler, not a stage1+ compiler. None of these tools actually need to be
staged at all, so they'll exhibit consistent behavior across the stages.
The android-copy-libs step is crucial for running tests on the Android target as
it copies necessary scripts and such to the emulator. We must run that before
running any tests there, but we erroneously only did it for compiletest test
suites!
This commit adds a new entry to the Travis matrix which performs a "distcheck",
which basically means that we create a tarball, extract that tarball, and then
build/test inside there. This ensures that the tarballs we produce are actually
able to be built/tested!
Along the way this also updates the rustbuild distcheck definition to propagate
the configure args from the top-level invocation.
Closes#38691
The source tarball creation step would attempt to skip a number of files that we
want to ignore ourselves, but once we've hit the vendor directory we don't want
to skip anything so be sure to vendor everything inside that directory.
Closes#38690
This commit changes all tools and such to get compiled in stage0, not in
later stages. The purpose of this commit is to cut down dependencies on later
stages for future modifications to the build system. Notably we're going to be
adding builders that produce a full suite of cross-compiled artifacts for a
particular host, and that shouldn't compile the `x86_64-unknown-linux-gnu`
compiler more than once. Currently dependencies on, for example, the error index
end up compiling the `x86_64-unknown-linux-gnu` compiler more than necessary.
As a result here we move many dependencies on these tools to being produced by a
stage0 compiler, not a stage1+ compiler. None of these tools actually need to be
staged at all, so they'll exhibit consistent behavior across the stages.
rustbuild: Move pretty test suites to host-only
In an ongoing effort to optimize the runtime of the Android cross builder this
commit updates the pretty test suites to run only for host platforms, not for
target platforms as well. This means we'll still keep running all the suites but
we'll only run them for configured hosts, not for configured targets. This
notably means that we won't be running these suites on Android or musl targets,
for example.
rustbuild: Compile rustc twice, not thrice
This commit switches the rustbuild build system to compiling the
compiler twice for a normal bootstrap rather than the historical three
times.
Rust is a bootstrapped language which means that a previous version of
the compiler is used to build the next version of the compiler. Over
time, however, we change many parts of compiler artifacts such as the
metadata format, symbol names, etc. These changes make artifacts from
one compiler incompatible from another compiler. Consequently if a
compiler wants to be able to use some artifacts then it itself must have
compiled the artifacts.
Historically the rustc build system has achieved this by compiling the
compiler three times:
* An older compiler (stage0) is downloaded to kick off the chain.
* This compiler now compiles a new compiler (stage1)
* The stage1 compiler then compiles another compiler (stage2)
* Finally, the stage2 compiler needs libraries to link against, so it
compiles all the libraries again.
This entire process amounts in compiling the compiler three times.
Additionally, this process always guarantees that the Rust source tree
can compile itself because the stage2 compiler (created by a freshly
created compiler) would successfully compile itself again. This
property, ensuring Rust can compile itself, is quite important!
In general, though, this third compilation is not required for general
purpose development on the compiler. The third compiler (stage2) can
reuse the libraries that were created during the second compile. In
other words, the second compilation can produce both a compiler and the
libraries that compiler will use. These artifacts *must* be compatible
due to the way plugins work today anyway, and they were created by the
same source code so they *should* be compatible as well.
So given all that, this commit switches the default build process to
only compile the compiler two times, avoiding this third compilation
by copying artifacts from the previous one. Along the way a new entry in
the Travis matrix was also added to ensure that our full bootstrap can
succeed. This entry does not run tests, though, as it should not be
necessary.
To restore the old behavior of a full bootstrap (three compiles) you can
either pass:
./configure --enable-full-bootstrap
or if you're using config.toml:
[build]
full-bootstrap = true
Overall this will hopefully be an easy 33% win in build times of the
compiler. If we do 33% less work we should be 33% faster! This in turn
should affect cycle times and such on Travis and AppVeyor positively as
well as making it easier to work on the compiler itself.
PTX support, take 2
- You can generate PTX using `--emit=asm` and the right (custom) target. Which
then you can run on a NVIDIA GPU.
- You can compile `core` to PTX. [Xargo] also works and it can compile some
other crates like `collections` (but I doubt all of those make sense on a GPU)
[Xargo]: https://github.com/japaric/xargo
- You can create "global" functions, which can be "called" by the host, using
the `"ptx-kernel"` ABI, e.g. `extern "ptx-kernel" fn kernel() { .. }`. Every
other function is a "device" function and can only be called by the GPU.
- Intrinsics like `__syncthreads()` and `blockIdx.x` are available as
`"platform-intrinsics"`. These intrinsics are *not* in the `core` crate but
any Rust user can create "bindings" to them using an `extern
"platform-intrinsics"` block. See example at the end.
- Trying to emit PTX with `-g` (debuginfo); you get an LLVM error. But I don't
think PTX can contain debuginfo anyway so `-g` should be ignored and a warning
should be printed ("`-g` doesn't work with this target" or something).
- "Single source" support. You *can't* write a single source file that contains
both host and device code. I think that should be possible to implement that
outside the compiler using compiler plugins / build scripts.
- The equivalent to CUDA `__shared__` which it's used to declare memory that's
shared between the threads of the same block. This could be implemented using
attributes: `#[shared] static mut SCRATCH_MEMORY: [f32; 64]` but hasn't been
implemented yet.
- Built-in targets. This PR doesn't add targets to the compiler just yet but one
can create custom targets to be able to emit PTX code (see the example at the
end). The idea is to have people experiment with this feature before
committing to it (built-in targets are "insta-stable")
- All functions must be "inlined". IOW, the `.rlib` must always contain the LLVM
bitcode of all the functions of the crate it was produced from. Otherwise, you
end with "undefined references" in the final PTX code but you won't get *any*
linker error because no linker is involved. IOW, you'll hit a runtime error
when loading the PTX into the GPU. The workaround is to use `#[inline]` on
non-generic functions and to never use `#[inline(never)]` but this may not
always be possible because e.g. you could be relying on third party code.
- Should `--emit=asm` generate a `.ptx` file instead of a `.s` file?
TL;DR Use Xargo to turn a crate into a PTX module (a `.s` file). Then pass that
PTX module, as a string, to the GPU and run it.
The full code is in [this repository]. This section gives an overview of how to
run Rust code on a NVIDIA GPU.
[this repository]: https://github.com/japaric/cuda
- Create a custom target. Here's the 64-bit NVPTX target (NOTE: the comments
are not valid because this is supposed to be a JSON file; remove them before
you use this file):
``` js
// nvptx64-nvidia-cuda.json
{
"arch": "nvptx64", // matches LLVM
"cpu": "sm_20", // "oldest" compute capability supported by LLVM
"data-layout": "e-i64:64-v16:16-v32:32-n16:32:64",
"llvm-target": "nvptx64-nvidia-cuda",
"max-atomic-width": 0, // LLVM errors with any other value :-(
"os": "cuda", // matches LLVM
"panic-strategy": "abort",
"target-endian": "little",
"target-pointer-width": "64",
"target-vendor": "nvidia", // matches LLVM -- not required
}
```
(There's a 32-bit target specification in the linked repository)
- Write a kernel
``` rust
extern "platform-intrinsic" {
fn nvptx_block_dim_x() -> i32;
fn nvptx_block_idx_x() -> i32;
fn nvptx_thread_idx_x() -> i32;
}
/// Copies an array of `n` floating point numbers from `src` to `dst`
pub unsafe extern "ptx-kernel" fn memcpy(dst: *mut f32,
src: *const f32,
n: usize) {
let i = (nvptx_block_dim_x() as isize)
.wrapping_mul(nvptx_block_idx_x() as isize)
.wrapping_add(nvptx_thread_idx_x() as isize);
if (i as usize) < n {
*dst.offset(i) = *src.offset(i);
}
}
```
- Emit PTX code
```
$ xargo rustc --target nvptx64-nvidia-cuda --release -- --emit=asm
Compiling core v0.0.0 (file://..)
(..)
Compiling nvptx-builtins v0.1.0 (https://github.com/japaric/nvptx-builtins)
Compiling kernel v0.1.0
$ cat target/nvptx64-nvidia-cuda/release/deps/kernel-*.s
//
// Generated by LLVM NVPTX Back-End
//
.version 3.2
.target sm_20
.address_size 64
// .globl memcpy
.visible .entry memcpy(
.param .u64 memcpy_param_0,
.param .u64 memcpy_param_1,
.param .u64 memcpy_param_2
)
{
.reg .pred %p<2>;
.reg .s32 %r<5>;
.reg .s64 %rd<12>;
ld.param.u64 %rd7, [memcpy_param_2];
mov.u32 %r1, %ntid.x;
mov.u32 %r2, %ctaid.x;
mul.wide.s32 %rd8, %r2, %r1;
mov.u32 %r3, %tid.x;
cvt.s64.s32 %rd9, %r3;
add.s64 %rd10, %rd9, %rd8;
setp.ge.u64 %p1, %rd10, %rd7;
@%p1 bra LBB0_2;
ld.param.u64 %rd3, [memcpy_param_0];
ld.param.u64 %rd4, [memcpy_param_1];
cvta.to.global.u64 %rd5, %rd4;
cvta.to.global.u64 %rd6, %rd3;
shl.b64 %rd11, %rd10, 2;
add.s64 %rd1, %rd6, %rd11;
add.s64 %rd2, %rd5, %rd11;
ld.global.u32 %r4, [%rd2];
st.global.u32 [%rd1], %r4;
LBB0_2:
ret;
}
```
- Run it on the GPU
``` rust
// `kernel.ptx` is the `*.s` file we got in the previous step
const KERNEL: &'static str = include_str!("kernel.ptx");
driver::initialize()?;
let device = Device(0)?;
let ctx = device.create_context()?;
let module = ctx.load_module(KERNEL)?;
let kernel = module.function("memcpy")?;
let h_a: Vec<f32> = /* create some random data */;
let h_b = vec![0.; N];
let d_a = driver::allocate(bytes)?;
let d_b = driver::allocate(bytes)?;
// Copy from host to GPU
driver::copy(h_a, d_a)?;
// Run `memcpy` on the GPU
kernel.launch(d_b, d_a, N)?;
// Copy from GPU to host
driver::copy(d_b, h_b)?;
// Verify
assert_eq!(h_a, h_b);
// `d_a`, `d_b`, `h_a`, `h_b` are dropped/freed here
```
---
cc @alexcrichton @brson @rkruppe
> What has changed since #34195?
- `core` now can be compiled into PTX. Which makes it very easy to turn `no_std`
crates into "kernels" with the help of Xargo.
- There's now a way, the `"ptx-kernel"` ABI, to generate "global" functions. The
old PR required a manual step (it was hack) to "convert" "device" functions
into "global" functions. (Only "global" functions can be launched by the host)
- Everything is unstable. There are not "insta stable" built-in targets this
time (\*). The users have to use a custom target to experiment with this
feature. Also, PTX instrinsics, like `__syncthreads` and `blockIdx.x`, are now
implemented as `"platform-intrinsics"` so they no longer live in the `core`
crate.
(\*) I'd actually like to have in-tree targets because that makes this target
more discoverable, removes the need to lug around .json files, etc.
However, bundling a target with the compiler immediately puts it in the path
towards stabilization. Which gives us just two cycles to find and fix any
problem with the target specification. Afterwards, it becomes hard to tweak
the specification because that could be a breaking change.
A possible solution could be "unstable built-in targets". Basically, to use an
unstable target, you'll have to also pass `-Z unstable-options` to the compiler.
And unstable targets, being unstable, wouldn't be available on stable.
> Why should this be merged?
- To let people experiment with the feature out of tree. Having easy access to
the feature (in every nightly) allows this. I also think that, as it is, it
should be possible to start prototyping type-safe single source support using
build scripts, macros and/or plugins.
- It's a straightforward implementation. No different that adding support for
any other architecture.
This commit relegates all pretty tests to not get run by default and rather get
run as part of an "aux" test suite. This "aux" suite is renamed from the old
"cargotest" suite to just collect tests that don't need to run everywhere but
should at least pass on Unix/Windows.
In an ongoing effort to optimize the runtime of the Android cross builder this
commit updates the pretty test suites to run only for host platforms, not for
target platforms as well. This means we'll still keep running all the suites but
we'll only run them for configured hosts, not for configured targets. This
notably means that we won't be running these suites on Android or musl targets,
for example.
This commit switches the rustbuild build system to compiling the
compiler twice for a normal bootstrap rather than the historical three
times.
Rust is a bootstrapped language which means that a previous version of
the compiler is used to build the next version of the compiler. Over
time, however, we change many parts of compiler artifacts such as the
metadata format, symbol names, etc. These changes make artifacts from
one compiler incompatible from another compiler. Consequently if a
compiler wants to be able to use some artifacts then it itself must have
compiled the artifacts.
Historically the rustc build system has achieved this by compiling the
compiler three times:
* An older compiler (stage0) is downloaded to kick off the chain.
* This compiler now compiles a new compiler (stage1)
* The stage1 compiler then compiles another compiler (stage2)
* Finally, the stage2 compiler needs libraries to link against, so it
compiles all the libraries again.
This entire process amounts in compiling the compiler three times.
Additionally, this process always guarantees that the Rust source tree
can compile itself because the stage2 compiler (created by a freshly
created compiler) would successfully compile itself again. This
property, ensuring Rust can compile itself, is quite important!
In general, though, this third compilation is not required for general
purpose development on the compiler. The third compiler (stage2) can
reuse the libraries that were created during the second compile. In
other words, the second compilation can produce both a compiler and the
libraries that compiler will use. These artifacts *must* be compatible
due to the way plugins work today anyway, and they were created by the
same source code so they *should* be compatible as well.
So given all that, this commit switches the default build process to
only compile the compiler three times, avoiding this third compilation
by copying artifacts from the previous one. Along the way a new entry in
the Travis matrix was also added to ensure that our full bootstrap can
succeed. This entry does not run tests, though, as it should not be
necessary.
To restore the old behavior of a full bootstrap (three compiles) you can
either pass:
./configure --enable-full-bootstrap
or if you're using config.toml:
[build]
full-bootstrap = true
Overall this will hopefully be an easy 33% win in build times of the
compiler. If we do 33% less work we should be 33% faster! This in turn
should affect cycle times and such on Travis and AppVeyor positively as
well as making it easier to work on the compiler itself.
A new option is introduced under the `[llvm]` section of `config.toml`,
`targets`, for overriding the list of LLVM targets to build support for.
The option is passed through to LLVM configure script. Also notes are
added about the implications of (ab)using the option; since the default
is not changed, and users of the option are expected to know what
they're doing anyway (as every porter should), the impact should be
minimal.
Fixes#38200.
rustbuild: Hotfix to unbreak nightly
Fixes an oversight unnoticed in #38468 that eventually broke nightly packaging. I didn't realize this until some moments ago, when I finally found out the failure is actually deterministic. Many apologies for eating 3 nightlies during the holidays.
r? @alexcrichton
Teach `rustdoc --test` about `--sysroot`, pass it when testing rust
This permits rustdoc tests to work in stage0.
Logical continuation of #36586.
Snippet from https://github.com/rust-lang/rust/issues/38575#issuecomment-269090724:
> it should actually be possible to run all the libstd tests immediately after creating std of stage0-out - there's no reason to build librustc at all if you've just made a change to (for example) libcollections, `./x.py test src/libcollections --stage 0 -v --incremental` should just work
This PR makes it so (or appears to in my testing).
r? @alexcrichton
`arr` is the actual list of targets participating in steps construction,
but due to #38468 the hosts array now consists of only the build triple
for the `dist` steps, hence all non-build-triple targets are lost for
the host-only rules.
Fix this by using the original non-shadowed hosts array in `arr`
calculation. This should unbreak the nightly packaging process.
Fixes#38637.
The comment touched, as originally written, only concerned itself with
the `test` steps. However, since #38468 the `arr` variable actually has
gained an indirect relationship with the `dist` steps too. The comment
failed to convey the extra meaning, contributing to the misunderstanding
which eventually lead to #38637. Fix that by moving the comment into the
right place near the relevant condition, and properly documenting
`arr`'s purpose.
- `--emit=asm --target=nvptx64-nvidia-cuda` can be used to turn a crate
into a PTX module (a `.s` file).
- intrinsics like `__syncthreads` and `blockIdx.x` are exposed as
`"platform-intrinsics"`.
- "cabi" has been implemented for the nvptx and nvptx64 architectures.
i.e. `extern "C"` works.
- a new ABI, `"ptx-kernel"`. That can be used to generate "global"
functions. Example: `extern "ptx-kernel" fn kernel() { .. }`. All
other functions are "device" functions.
initial SPARC support
### UPDATE
Can now compile `no_std` executables with:
```
$ cargo new --bin app && cd $_
$ edit Cargo.toml && tail -n2 $_
[dependencies]
core = { path = "/path/to/rust/src/libcore" }
$ edit src/main.rs && cat $_
#![feature(lang_items)]
#![no_std]
#![no_main]
#[no_mangle]
pub fn _start() -> ! {
loop {}
}
#[lang = "panic_fmt"]
fn panic_fmt() -> ! {
loop {}
}
$ edit sparc-none-elf.json && cat $_
{
"arch": "sparc",
"data-layout": "E-m:e-p:32:32-i64:64-f128:64-n32-S64",
"executables": true,
"llvm-target": "sparc",
"os": "none",
"panic-strategy": "abort",
"target-endian": "big",
"target-pointer-width": "32"
}
$ cargo rustc --target sparc-none-elf -- -C linker=sparc-unknown-elf-gcc -C link-args=-nostartfiles
$ file target/sparc-none-elf/debug/app
app: ELF 32-bit MSB executable, SPARC, version 1 (SYSV), statically linked, not stripped
$ sparc-unknown-elf-readelf -h target/sparc-none-elf/debug/app
ELF Header:
Magic: 7f 45 4c 46 01 02 01 00 00 00 00 00 00 00 00 00
Class: ELF32
Data: 2's complement, big endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: EXEC (Executable file)
Machine: Sparc
Version: 0x1
Entry point address: 0x10074
Start of program headers: 52 (bytes into file)
Start of section headers: 1188 (bytes into file)
Flags: 0x0
Size of this header: 52 (bytes)
Size of program headers: 32 (bytes)
Number of program headers: 2
Size of section headers: 40 (bytes)
Number of section headers: 14
Section header string table index: 11
$ sparc-unknown-elf-objdump -Cd target/sparc-none-elf/debug/app
target/sparc-none-elf/debug/app: file format elf32-sparc
Disassembly of section .text:
00010074 <_start>:
10074: 9d e3 bf 98 save %sp, -104, %sp
10078: 10 80 00 02 b 10080 <_start+0xc>
1007c: 01 00 00 00 nop
10080: 10 80 00 02 b 10088 <_start+0x14>
10084: 01 00 00 00 nop
10088: 10 80 00 00 b 10088 <_start+0x14>
1008c: 01 00 00 00 nop
```
---
Someone wants to attempt launching some Rust [into space](https://www.reddit.com/r/rust/comments/5h76oa/c_interop/) but their platform is based on the SPARCv8 architecture. Let's not block them by enabling LLVM's SPARC backend.
Something very important that they'll also need is the "cabi" stuff as they'll be embedding some Rust code into a bigger C application (i.e. heavy use of `extern "C"`). The question there is what name(s) should we use for "target_arch" as the "cabi" implementation [varies according to that parameter](https://github.com/rust-lang/rust/blob/1.13.0/src/librustc_trans/abi.rs#L498-L523).
AFAICT, SPARCv8 is a 32-bit architecture and SPARCv9 is a 64-bit architecture. And, LLVM uses `sparc`, `sparcv9` and `sparcel` for [the architecture triple](ac1c94226e/include/llvm/ADT/Triple.h (L67-L69)) so perhaps we should use `target_arch = "sparc"` (32-bit) and `target_arch = "sparcv9"` (64-bit) as well.
r? @alexcrichton This PR only enables this LLVM backend when rustbuild is used. Do I also need to implement this for the old Makefile-based build system? Or are all our nightlies now being generated using rustbuild?
cc @brson
rustbuild: Actually test musl on the musl bot
A typo unfortunately meant that we haven't been testing musl for a bit, so now
it's time to discover if we accidentally introduced a regression!
rustbuild: Run debuginfo tests by default
This fixes an accidental regression in rustbuild which stopped running debuginfo
tests by default. Here we flag the test suites as `default(true)` to ensure that
they're run on bots, for example.
rustbuild: Update Cargo download location
I updated the beta compiler used to bootstrap the master branch in #38438 with
the intention of fixing Travis OSX linkage issues but I mistakenly forgot that
the PR only updated rustc, not Cargo itself. Cargo has a new release process
with downloads in a different location, so this commit updates rustbuild to
download from this new location by tracking revisions instead of Cargo nightly
dates.
rustbuild: Eliminate duplication of dist tarballs
Fixes#38365 by not constructing the duplicate steps in the first place, as suggested. The source package step is lacking the check as in other steps, so it is added as well.
Tested locally with the `alexcrichton/rust-slave-linux-cross:2016-11-11` container (with the build slave init replaced with no-op, of course).
r? @alexcrichton
adaptation to rustbuild for openbsd
Since the switch to rustbuild, the build for openbsd is broken:
- [X] `ar` inference based on compiler name is wrong (OpenBSD usually use `egcc`, but `ear` doesn't exist)
- [X] `make` isn't GNU-make under OpenBSD (and others BSD platforms)
- [x] `stdc++` isn't the right stdc++ library to link with (it should be `estdc++`)
- [x] corrects tests that don't pass anymore (problems related to rustbuild)
r? @alexcrichton
rustbuild: Stop building docs for libtest by default
They cause the search index from the std docs to get overwritten just like #34800.
Part of #38319.
Add prefix to config.toml
This allows `rustbuild` to be used to install to a prefix.
```toml
[build]
prefix = "/path/to/install"
```
For example, the following `config.toml` will cause `x.py dist --install` to install to `/path/to/install`
This fixes an accidental regression in rustbuild which stopped running debuginfo
tests by default. Here we flag the test suites as `default(true)` to ensure that
they're run on bots, for example.
