[llvm] Fix signal handling for platforms without SA_ONSTACK (PR #118962)

[Artem Belevich via llvm-commits]

Artem-B wrote:

Check who made meaningful commits to https://github.com/llvm/llvm-project/blob/main/llvm/lib/Support/Unix/Signals.inc and who reviewed those changes. That would be a good starting point.

https://github.com/llvm/llvm-project/pull/118962