…ernally.

… an easy-to-overlook warning otherwise.

…ng-based run-make tests to use PGO.

It's just a waste of memory. This also gets rid of the special case for
"".

…lexcrichton

PGO - Add a smoketest for combining PGO with cross-language LTO.

This PR

- Adds a test making sure that PGO can be combined with cross-language LTO.
- Does a little cleanup on how the `pgo-use` flag is handled internally.
- Makes the compiler error if the `pgo-use` file given to `rustc` doesn't actually exist. LLVM only gives a warning and then just doesn't do PGO. Clang, on the other hand, does give an error in this case.
- Makes the build system also build `compiler-rt` when building LLDB. This way the Clang compiler that we get from building LLDB can perform PGO, which is something that the new test case wants to do. CI compile times shouldn't be affected too much.

…henkov

Don't arena-allocate static symbols.

It's just a waste of memory. This also gets rid of the special case for
"".

r? @petrochenkov

Ship profiler with windows-gnu

Fixes rust-lang#49409

I don't know if we can enable it for testing, windows-gnu jobs are already taking too long: rust-lang#59637.

r? @michaelwoerister

P.S.
I have tested only x86_64 build.

Fix spelling in release notes

MaybeUninit doctest: remove unnecessary type ascription