Clean up StopTheWorld code after r192686.

Remove outdated comments. Also remove code that handled an issue in libc's
sigaction(), which we don't use anymore.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@192689 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed