build: add entt library

include/entt/stl/concepts.hpp

@@ -0,0 +1,24 @@
+#ifndef ENTT_STL_CONCEPTS_HPP
+#define ENTT_STL_CONCEPTS_HPP
+
+/*! @cond ENTT_INTERNAL */
+#if __has_include(<entt/ext/stl/concepts.hpp>)
+#    include <entt/ext/stl/concepts.hpp>
+#else
+#    include <concepts>
+
+namespace entt::stl {
+
+using std::constructible_from;
+using std::default_initializable;
+using std::derived_from;
+using std::integral;
+using std::invocable;
+using std::same_as;
+using std::unsigned_integral;
+
+} // namespace entt::stl
+#endif
+/*! @endcond */
+
+#endif