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

[Rainer Orth via llvm-commits]

rorth wrote:

This patch broke the [Solaris/amd64 buildbot](https://lab.llvm.org/staging/#/builders/94/builds/5085).  Solaris currently lacks `internal_sigdelset` (and some other non-Linux targets probably too).

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