[analyzer] PthreadLockChecker: model failed pthread_mutex_destroy() calls.

pthread_mutex_destroy() may fail, returning a non-zero error number, and
keeping the mutex untouched. The mutex can be used on the execution branch
that follows such failure, so the analyzer shouldn't warn on using
a mutex that was previously destroyed, when in fact the destroy call has failed.

Patch by Malhar Thakkar!

Differential revision: https://reviews.llvm.org/D32449

llvm-svn: 304159