stl: refine memory.hpp

src/entt/stl/memory.hpp

@@ -1,6 +1,10 @@
 #ifndef ENTT_STL_MEMORY_HPP
 #define ENTT_STL_MEMORY_HPP
 
+#include <memory>
+#include <type_traits>
+#include <utility>
+
 namespace entt::stl {
 
 /*! @cond TURN_OFF_DOXYGEN */
@@ -22,16 +26,16 @@ template<typename Type>
 #    include <version>
 #
 #    if defined(__cpp_lib_to_address)
-#        include <memory>
-using std::to_address;
-#    else
-using stl::internal::to_address;
+#        define ENTT_STL_TO_ADDRESS std::to_address
 #    endif
-#
-#else
-using stl::internal;
 #endif
 
+#ifndef ENTT_STL_TO_ADDRESS
+#    define ENTT_STL_TO_ADDRESS internal::to_address
+#endif
+
+using ENTT_STL_TO_ADDRESS;
+
 } // namespace entt::stl
 
 #endif