[clang] [clang-tools-extra] [llvm] [LLVM][CLANG] Update signal-handling behavior to comply with POSIX (PR #169340)

[Xing Xue via cfe-commits]

xingxue-ibm wrote:

> I get the feeling this change is over broad, as I note in my other comments. It changes the signal handling behaviour for way more than just the utilities that would be required by POSIX, it touches every consumer of the signal handling support.
> 
> I think a more targeted approach would be appropriate, with either an opt-in or out for the utilities which mandate the POSIX behaviour.

Good point, thanks! I’ve changed patch to target `clang` only, which is included in the POSIX conformance test.

https://github.com/llvm/llvm-project/pull/169340