Add a script that is used to deflake inherently flaky tsan tests.
It is invoked from lit tests as:
%deflake %run %t
The script runs the target program up to 10 times,
until it produces a tsan warning.
llvm-svn: 209898
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
llvm-svn: 203648