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

[Dmitry Vyukov via llvm-commits]

dvyukov wrote:

I agree we messed signal mask on recursive signals.
This code is tricky and fragile, I always afraid of touching it. But I don't see anything obviously wrong with this change. It probably should be OK to call internal allocator at that point.

I think LongJmp function should also pop from the vector to restore the original size captured in SetJmp.

Please also run all signal-related tests multiple times.

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