tsan: fix handling of pthread_cond_wait in presence of pthread_cancel
if the thread is cancelled in pthread_cond_wait, it locks the mutex before
processing pthread_cleanup stack
but tsan was missing that, thus reporting false double-lock/wrong-unlock errors
see the test for details



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@203648 91177308-0d34-0410-b5e6-96231b3b80d8