Move platform support to the rustc book.
This moves the [Platform Support](https://forge.rust-lang.org/release/platform-support.html) page from the forge to the rustc book. There are several reasons for doing this:
* The forge is not really oriented towards end-users (it mostly contains infrastructure, governance and policy, internal team pages, etc.). This platform support page is useful to user to know which targets are supported.
* This page can now be updated in-sync with any PRs that add or remove a target, or change its status.
* This is now automatically checked on CI to verify the list does not get out of sync. Currently it only checks the presence/absence of an entry, but more sophisticated checks could be added in the future.
I'm not 100% certain this is the best location, but I think it fits. I'd like to see the rustc guide continue to grow, including things like linking information and more platform-specific details.
A few updates:
- Some minor wording and formatting changes.
- Remove the `cargo` column.
- Explain the columns up-front.
- Add no-wrap on the target-triple, which looks better to me.
- Minor mention on how to install support for a built-in target via rustup.
Stabilize control-flow-guard codegen option
This is the stabilization PR discussed in #68793. It converts the `-Z control-flow-guard` debugging option into a codegen option (`-C control-flow-guard`), and changes the associated tests.
Add `format_args_capture` feature
This is the initial implementation PR for [RFC 2795](https://github.com/rust-lang/rfcs/pull/2795).
Note that, as dicussed in the tracking issue (#67984), the feature gate has been called `format_args_capture`.
Next up I guess I need to add documentation for this feature. I've not written any docs before for rustc / std so I would appreciate suggestions on where I should add docs.
Fix handling of reserved registers for ARM inline asm
`r6` is now disallowed as an operand since LLVM sometimes uses it as a base pointer.
The check against using the frame pointer as an operand now takes the platform into account and will block either `r7` or `r11` as appropriate.
Fixes#73450
cc @cbiffle
Diagnose use of incompatible sanitizers
Emit an error when incompatible sanitizer are configured through command
line options. Previously the last one configured prevailed and others
were silently ignored.
Additionally use a set to represent configured sanitizers, making it
possible to enable multiple sanitizers at once. At least in principle,
since currently all of them are considered to be incompatible with
others.
asm: Allow multiple template string arguments; interpret them as newline-separated
Allow the `asm!` macro to accept a series of template arguments, and interpret them as if they were concatenated with a '\n' between them. This allows writing an `asm!` where each line of assembly appears in a separate template string argument.
This syntax makes it possible for rustfmt to reliably format and indent each line of assembly, without risking changes to the inside of a template string. It also avoids the complexity of having the user carefully format and indent a multi-line string (including where to put the surrounding quotes), and avoids the extra indentation and lines of a call to `concat!`.
For example, rewriting the second example from the [blog post on the new inline assembly syntax](https://blog.rust-lang.org/inside-rust/2020/06/08/new-inline-asm.html) using multiple template strings:
```rust
fn main() {
let mut bits = [0u8; 64];
for value in 0..=1024u64 {
let popcnt;
unsafe {
asm!(
" popcnt {popcnt}, {v}",
"2:",
" blsi rax, {v}",
" jz 1f",
" xor {v}, rax",
" tzcnt rax, rax",
" stosb",
" jmp 2b",
"1:",
v = inout(reg) value => _,
popcnt = out(reg) popcnt,
out("rax") _, // scratch
inout("rdi") bits.as_mut_ptr() => _,
);
}
println!("bits of {}: {:?}", value, &bits[0..popcnt]);
}
}
```
Note that all the template strings must appear before all other arguments; you cannot, for instance, provide a series of template strings intermixed with the corresponding operands.
