[compiler-rt] [sanitizer_common] Block asynchronous signals only (PR #98200)

[Vitaly Buka via llvm-commits]

vitalybuka wrote:

> @vitalybuka Right. I verified that removing [this line](https://github.com/llvm/llvm-project/pull/98200/files#diff-f740809540e5357d610d6a34715a57e3be96ccf85736f04a3092aa0a0728b2caR182) fixes the issue. Maybe we can make it conditional?

We should just update sigmask more carefully, we just somehow missed this.
@thurstond would you be able to work on this next week?

https://github.com/llvm/llvm-project/pull/98200