support OCaml 5.3

Author: anmonteiro

lib/top/compat_top.ml

@@ -96,7 +96,11 @@ let extension_constructor
   ; ext_private
   ; ext_loc
   ; ext_attributes
-#if OCAML_VERSION >= (4, 11, 0)
+#if OCAML_VERSION >= (5, 3, 0)
+  ; ext_uid = Uid.mk
+      ~current_unit:
+        (Some (Unit_info.make ~source_file:"mdx.ml" Impl "mdx"))
+#elif OCAML_VERSION >= (4, 11, 0)
   ; ext_uid = Uid.mk ~current_unit:"mdx"
 #endif
   }