Fix optional compilation of ocamliface.

ocamliface/dune

@@ -28,10 +28,22 @@ let () =
    from
    (ocaml-compiler-libs.common -> mlstub.real.ml)
    (-> mlstub.empty.ml))
+  (select mltypes.ml
+    from
+    (ocaml-compiler-libs.common -> mltypes.real.ml)
+    (-> mltypes.empty.ml))
+    (select mltypes.mli
+    from
+    (ocaml-compiler-libs.common -> mltypes.real.mli)
+    (-> mltypes.empty.mli))
+     (select mlcompat.ml
+    from
+    (ocaml-compiler-libs.common -> mlcompat.real.ml)
+    (-> mlcompat.empty.ml))
  ))
 
 (rule
  (action
-  (copy# mlcompat_%s.ml mlcompat.ml)))
+  (copy# mlcompat_%s.ml mlcompat.real.ml)))
 |} suffix)
-;;
\ No newline at end of file
+;;