Don't trigger an assertion failure when loading the shim location module.

ocamliface/4.02/location.ml

@@ -40,7 +40,7 @@ let show_filename = dummy
 let absname = ref true
 let report_exception = dummy
 let report_error = dummy
-let register_error_of_exn = dummy
+let register_error_of_exn _ = ()
 let error_of_exn = dummy
 let error_of_printer_file = dummy
 let error_of_printer = dummy