tsan: treat SIGSYS as synchronous signal
It is required for chromium sandboxing code.
From the description it seems to be indeed synchronous -- called back on syscall with incorrect arguments,
but seems to be unused in practice. So this should be fine.



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@186579 91177308-0d34-0410-b5e6-96231b3b80d8