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

[Valery Chernov via llvm-commits]

vvchernov 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.

Hello @Artem-B! May be do you know who can review it?

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