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

[Artem Belevich via llvm-commits]

Artem-B wrote:

I have no context for this change. Based on the folks CC'ed, it may have something to do with NVPTX back-end, but I don't quite see how it may be related to QNX.


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