Implement LWG issue #2135. If something goes wrong in condition_variable::wait, call terminate() rather than throwing an error. Do this indirectly, by marking the call as 'noexcept'. This is better than just calling terminate() directly, because it gives a better error message on the console.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@204778 91177308-0d34-0410-b5e6-96231b3b80d8