Update variant "all types same/convertible" metaprogramming (#3070)

Author: CaseyCarter

stl/inc/type_traits

@@ -1619,11 +1619,12 @@ template <class _From, class _To, class = void>
 struct _Invoke_convertible : false_type {};
 
 template <class _From, class _To>
-struct _Invoke_convertible<_From, _To, void_t<decltype(_Fake_copy_init<_To>(_Returns_exactly<_From>()))>> : true_type {
-};
+struct _Invoke_convertible<_From, _To, void_t<decltype(_STD _Fake_copy_init<_To>(_STD _Returns_exactly<_From>()))>>
+    : true_type {};
 
 template <class _From, class _To>
-struct _Invoke_nothrow_convertible : bool_constant<noexcept(_Fake_copy_init<_To>(_Returns_exactly<_From>()))> {};
+struct _Invoke_nothrow_convertible
+    : bool_constant<noexcept(_STD _Fake_copy_init<_To>(_STD _Returns_exactly<_From>()))> {};
 
 template <class _Result, bool _Nothrow>
 struct _Invoke_traits_common {