Patch contributed by Dev Dude for mingw64 port.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@162188 91177308-0d34-0410-b5e6-96231b3b80d8

src/memory.cpp

@@ -119,6 +119,8 @@ __shared_weak_count::__get_deleter(const type_info&) const _NOEXCEPT
 
 #endif  // _LIBCPP_NO_RTTI
 
+#if __has_feature(cxx_atomic)
+
 static const std::size_t __sp_mut_count = 16;
 static mutex mut_back[__sp_mut_count];
 
@@ -162,6 +164,7 @@ __get_sp_mut(const void* p)
     return muts[hash<const void*>()(p) & (__sp_mut_count-1)];
 }
 
+#endif // __has_feature(cxx_atomic)
 
 void
 declare_reachable(void*)