Merge to upstream r222492.

Change-Id: I6a0a6e90d217a69531ec3bb5ca0a367f39f4a1da

include/__mutex_base

@@ -22,6 +22,8 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+#ifndef _LIBCPP_HAS_NO_THREADS
+
 class _LIBCPP_TYPE_VIS mutex
 {
     pthread_mutex_t __m_;
@@ -315,6 +317,7 @@ private:
     void __do_timed_wait(unique_lock<mutex>& __lk,
        chrono::time_point<chrono::system_clock, chrono::nanoseconds>) _NOEXCEPT;
 };
+#endif // !_LIBCPP_HAS_NO_THREADS
 
 template <class _To, class _Rep, class _Period>
 inline _LIBCPP_INLINE_VISIBILITY
@@ -332,6 +335,7 @@ __ceil(chrono::duration<_Rep, _Period> __d)
     return __r;
 }
 
+#ifndef _LIBCPP_HAS_NO_THREADS
 template <class _Predicate>
 void
 condition_variable::wait(unique_lock<mutex>& __lk, _Predicate __pred)
@@ -396,6 +400,8 @@ condition_variable::wait_for(unique_lock<mutex>& __lk,
                       _VSTD::move(__pred));
 }
 
+#endif // !_LIBCPP_HAS_NO_THREADS
+
 _LIBCPP_END_NAMESPACE_STD
 
 #endif  // _LIBCPP___MUTEX_BASE