Use std::is_base_of_v instead of std::derived_from

Our use of `std::derived_from` reportedly fails with libc++ because we don't
include the `<concepts>` header. This change should fix the problem by just
using `std::is_base_of_v` instead, which has the advantage of not requiring
C++20.

Fixes #19364.

PiperOrigin-RevId: 702351498

Author: acozzette

src/google/protobuf/port.h

@@ -178,14 +178,9 @@ template <typename To, typename From>
 void AssertDownCast(From* from) {
   static_assert(std::is_base_of<From, To>::value, "illegal DownCast");
 
-#if defined(__cpp_concepts)
   // Check that this function is not used to downcast message types.
   // For those we should use {Down,Dynamic}CastTo{Message,Generated}.
-  static_assert(!requires {
-    std::derived_from<std::remove_pointer_t<To>,
-                      typename std::remove_pointer_t<To>::MessageLite>;
-  });
-#endif
+  static_assert(!std::is_base_of_v<MessageLite, To>);
 
 #if PROTOBUF_RTTI
   // RTTI: debug mode only!