[rtsan] Add test for pthread_cond_wait segfault (#150776)
Introduce the test from
https://github.com/llvm/llvm-project/issues/146120
For future readers of this PR, if this test causes a segfault please
comment out the line indicated by the comment (or revert this entire
commit).
My plan is to commit this, see if any test runners fail, then submit the
fix in a follow on.
I cannot repro this bug on my machine so I need some confirmation of the
bug being fixed as it is submitted.
