[compiler-rt] [tsan] Fix nested signal handling (PR #138599)

[Steven Wu via llvm-commits]

cachemeifyoucan wrote:

Test breaks Darwin Bots on iOSSim simulator: https://green.lab.llvm.org/job/llvm.org/job/clang-san-iossim/9036/testReport/ThreadSanitizer-x86_64-iossim/ThreadSanitizer-x86_64-iossim/signal_recursive_cpp/

I think the reason is that `sem_init` is deprecated on Darwin systems. I will mark the test as `UNSUPPORTED` for now.

https://github.com/llvm/llvm-project/pull/138599