Auto merge of #125165 - Oneirical:pgo-branch-weights, r=jieyouxu

Migrate `run-make/pgo-branch-weights` to `rmake`

Part of #121876 and the associated [Google Summer of Code project](https://blog.rust-lang.org/2024/05/01/gsoc-2024-selected-projects.html).

This is a scary one and I expect things to break. Set as draft, because this isn't ready.

- [x] There is this comment here, which suggests the test is excluded from the testing process due to a platform specific issue? I can't see anything here that would cause this test to not run...
> // FIXME(mati865): MinGW GCC miscompiles compiler-rt profiling library but with Clang it works
// properly. Since we only have GCC on the CI ignore the test for now."

EDIT: This is specific to Windows-gnu.

- [x] The Makefile has this line:
```
ifneq (,$(findstring x86,$(TARGET)))
COMMON_FLAGS=-Clink-args=-fuse-ld=gold
```
I honestly can't tell whether this is checking if the target IS x86, or IS NOT. EDIT: It's checking if it IS x86.

- [x] I don't know why the Makefile was trying to pass an argument directly in the Makefile instead of setting that "aaaaaaaaaaaa2bbbbbbbbbbbb2bbbbbbbbbbbbbbbbcc" input as a variable in the Rust program directly. I changed that, let me know if that was wrong.

- [x] Trying to rewrite `cat "$(TMPDIR)/interesting.ll" | "$(LLVM_FILECHECK)" filecheck-patterns.txt` resulted in some butchery. For starters, in `tools.mk`, LLVM_FILECHECK corrects its own backslashes on Windows distributions, but there is no further mention of it, so I assume this is a preset environment variable... but is it really? Then, the command itself uses a Standard Input and a passed input file as an argument simultaneously, according to the [documentation](https://llvm.org/docs/CommandGuide/FileCheck.html#synopsis).

try-job: aarch64-gnu

Author: bors