and further simplify its checking in runtest

and its use cases in more detail

LLVM_PROFILER_RT_LIB may be set to an absolute path (e.g., in Fedora builds),
but `-l` expects a library name, not a path. After rust-lang#138273, this caused builds
to fail with a "could not find native static library" error.

This patch updates the build script to split the path into directory and
filename, using `cargo::rustc-link-search` for the directory and
`cargo::rustc-link-lib=+verbatim` for the file. This allows profiler_builtins to
correctly link the static library even when an absolute path is provided.

Also add a WCStr type

std: make `cmath` functions safe

The floating point intrinsics are more difficult, I'll probably wait until rust-lang#119899 has merged before making them safe as well.

compiletest: Make `SUGGESTION` annotations viral

If one of them is expected in a test file, then others should be annotated as well, in the same way as with `HELP`s and `NOTE`s.
This doesn't require much of an additional annotation burden, but simplifies the rules.

r? `@jieyouxu`

…th-fix, r=kobzol

Fix profiler_builtins build script to handle full path to profiler lib

LLVM_PROFILER_RT_LIB may be set to an absolute path (e.g., in Fedora builds), but `-l` expects a library name, not a path. After rust-lang#138273, this caused builds to fail with a "could not find native static library" error.

This patch updates the build script to split the path into directory and filename, using `cargo::rustc-link-search` for the directory and `cargo::rustc-link-lib=+verbatim` for the file. This allows profiler_builtins to correctly link the static library even when an absolute path is provided.

…=tgross35,joboet

Use `with_native_path` for Windows

Ideally, each platform should use their own native path type internally. This will, for example, allow passing a UTF-16 string directly to `std::fs::File::open` and therefore avoid the need for allocating a new null-terminated wide string. However, doing that for every function and platform all at once makes for a large PR that is way too prone to breaking. So this just does some of the Windows parts.

As with the previous Unix PR (rust-lang#138832) this is intended to be merely a refactoring so I've avoided anything that may require more substantial changes.

Document that `opt-dist` requires metrics to be enabled

Suggested in rust-lang#139686.