Explicitly qualify atomic_wait and atomic_notify function calls

Summary:
`std::atomic_wait()` and `std::atomic_notify_one()` are marked as unavailable.
Not really sure what that means, but it seems to be breaking some open source
builds facebook#1527.  Explicitly qualify the
calls into those functions to try and fix the build break.

Since we cannot conditionally import either of the above (because they are
marked as unavailable), we can't rely on the standard implementations.  To
prevent ADL from kicking in when the standard-library defines these, we fully
qualify these and use `tag_invoke` for the customization points used in tests.

Reviewed By: davidtgoldblatt

Differential Revision: D26742072

fbshipit-source-id: 9f44bbfd37530f5ecffa3e03d673cfb1df953299

folly/lang/CustomizationPoint.h

@@ -50,7 +50,7 @@
 namespace folly {
 
 // Using 'auto' for non-type template parameters is only possible from C++17
-#if __cplusplus >= 201703L
+#if FOLLY_CPLUSPLUS >= 201703L
 
 //  cpo_t<CPO>
 //
@@ -71,6 +71,6 @@ namespace folly {
 template <const auto& Tag>
 using cpo_t = std::decay_t<decltype(Tag)>;
 
-#endif // __cplusplus >= 201703L
+#endif // FOLLY_CPLUSPLUS >= 201703L
 
 } // namespace folly

folly/synchronization/AtomicNotification-inl.h

@@ -118,7 +118,6 @@ void atomic_notify_all_impl(const Atom<Integer, Args...>* atomic) {
   });
 }
 
-
 template <typename Integer>
 void tag_invoke(
     atomic_wait_fn, const std::atomic<Integer>* atomic, Integer expected) {

folly/synchronization/AtomicNotification.h

@@ -59,7 +59,7 @@ struct atomic_wait_fn {
 constexpr inline auto atomic_wait =
     detail::atomic_notification::atomic_wait_fn{};
 
-// mimic: std::atomic_wait_until, p1135r0
+//  mimic: std::atomic_wait_until, p1135r0
 namespace detail {
 namespace atomic_notification {
 struct atomic_wait_until_fn {