[sanitizer] Simplify sigaction and sigset_t handling.



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@189338 91177308-0d34-0410-b5e6-96231b3b80d8
[msan] A test for ppoll() interceptor.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@189339 91177308-0d34-0410-b5e6-96231b3b80d8