Move mandates check __atomic/{support.h -> atomic.h}

Author: dalg24

libcxx/include/__atomic/atomic.h

@@ -230,8 +230,14 @@ struct __atomic_waitable_traits<__atomic_base<_Tp, _IsIntegral> > {
   }
 };
 
+template <typename _Tp>
+struct __check_atomic_mandates {
+  using type = _Tp;
+  static_assert(is_trivially_copyable<_Tp>::value, "std::atomic<T> requires that 'T' be a trivially copyable type");
+};
+
 template <class _Tp>
-struct atomic : public __atomic_base<_Tp> {
+struct atomic : public __atomic_base<typename __check_atomic_mandates<_Tp>::type> {
   using __base _LIBCPP_NODEBUG = __atomic_base<_Tp>;
 
 #if _LIBCPP_STD_VER >= 20

libcxx/include/__atomic/support.h

@@ -111,13 +111,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-template <typename _Tp>
-struct __check_atomic_mandates {
-  using type = _Tp;
-  static_assert(is_trivially_copyable<_Tp>::value, "std::atomic<T> requires that 'T' be a trivially copyable type");
-};
-
-template <typename _Tp, typename _Base = __cxx_atomic_base_impl<typename __check_atomic_mandates<_Tp>::type> >
+template <typename _Tp, typename _Base = __cxx_atomic_base_impl<_Tp> >
 struct __cxx_atomic_impl : public _Base {
   _LIBCPP_HIDE_FROM_ABI __cxx_atomic_impl() _NOEXCEPT = default;
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __cxx_atomic_impl(_Tp __value) _NOEXCEPT : _Base(__value) {}