Do not define a `const` static variable as `constexpr`. While this is legal it

is not supported in all toolchains.

Should fix https://github.com/protocolbuffers/protobuf/issues/15030

PiperOrigin-RevId: 592574780

src/google/protobuf/message.cc

@@ -192,9 +192,10 @@ static std::string InitializationErrorStringImpl(const MessageLite& msg) {
   return DownCast<const Message&>(msg).InitializationErrorString();
 }
 
-constexpr MessageLite::DescriptorMethods Message::kDescriptorMethods = {
-    GetTypeNameImpl,
-    InitializationErrorStringImpl,
+PROTOBUF_CONSTINIT const MessageLite::DescriptorMethods
+    Message::kDescriptorMethods = {
+        GetTypeNameImpl,
+        InitializationErrorStringImpl,
 };
 
 namespace internal {