[compiler-rt] Test fixups for MSVC. (PR #109887)

[Martin Storsjö via llvm-commits]

https://github.com/mstorsjo commented:

I did a cursory review and pointed out a couple of issues I found, but I'd appreciate @vitalybuka's opinions too.

Regarding keeping these tests working in mingw configurations, I set up a github actions workflow that you can try out to run these tests - see the second commit at https://github.com/mstorsjo/llvm-project/commits/gha-mingw-compiler-rt. I tested your PR on top of it, with the following results: https://github.com/mstorsjo/llvm-project/actions/runs/11029615284/job/30632424312

(Ideally we'd have things like this integrated into regular precommit CI testing. I haven't tested running tests with clang-cl in similar configurations on github actions though.)

Finally, a small nit - the PR subject could use some tag to indicate that this is related to compiler-rt, to make it clearer once looking at the final commit as part of the whole commit log.

https://github.com/llvm/llvm-project/pull/109887