Implement RFC3137 trim-paths sysroot changes - take 2
This PR is a continuation of https://github.com/rust-lang/rust/pull/118149. Nothing really changed, except for https://github.com/rust-lang/rust/pull/129408 which I was able to trigger locally.
Original description:
> Implement parts of #111540
>
> Right now, backtraces into sysroot always shows /rustc/$hash in diagnostics, e.g.
>
> ```
> thread 'main' panicked at 'hello world', map-panic.rs:2:50
> stack backtrace:
> 0: std::panicking::begin_panic
> at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/panicking.rs:616:12
> 1: map_panic::main::{{closure}}
> at ./map-panic.rs:2:50
> 2: core::option::Option<T>::map
> at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/option.rs:929:29
> 3: map_panic::main
> at ./map-panic.rs:2:30
> 4: core::ops::function::FnOnce::call_once
> at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/ops/function.rs:248:5
> note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
> ```
>
> [RFC 3127 said](https://rust-lang.github.io/rfcs/3127-trim-paths.html#changing-handling-of-sysroot-path-in-rustc)
>
> > We want to change this behaviour such that, when rust-src source files can be discovered, the virtual path is discarded and therefore the local path will be embedded, unless there is a --remap-path-prefix that causes this local path to be remapped in the usual way.
>
> This PR implements this behaviour. When `rust-src` is present at compile time, rustc replaces /rustc/$hash with a real path into local rust-src with best effort. To sanitise this, users must explicitly supply `--remap-path-prefix=<path to rust-src>=foo`.
cc `@cbeuw`
Fix#105907Fix#85463
try-job: dist-x86_64-linux
try-job: x86_64-msvc
try-job: dist-x86_64-msvc
try-job: armhf-gnu
1d9162bced