tsan: fix signal handling in ignored libraries

The first issue is that we longjmp from ScopedInterceptor scope
when called from an ignored lib. This leaves thr->in_ignored_lib set.
This, in turn, disables handling of sigaction. This, in turn,
corrupts tsan state since signals delivered asynchronously.
Another issue is that we can ignore synchronization in asignal
handler, if the signal is delivered into an IgnoreSync region.
Since signals are generally asynchronous, they should ignore
memory access/synchronization/interceptor ignores.
This could lead to false positives in signal handlers.

llvm-svn: 261658