Make ~mutex and ~condition_variable trivial on Windows.

The implementations of __libcpp_mutex_destroy and __libcpp_condvar_destroy
are already NOPs, so this optimization is safe to perform.

See r365273 and PR27658 for more information.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@365281 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed