Revert "Revert "Implement std::condition_variable via pthread_cond_clockwait() where available""

With the fix for non-Linux.

This reverts commit c1c519d2f1a66dd2eeaa4c321d8d7b50f623eb71.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@372242 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed