fixup! Source maps: use ignoreList to hide runtime files

Author: vouillon

compiler/lib/js_output.ml

@@ -2162,8 +2162,7 @@ let program ?(accept_unnamed_var = false) f ?source_map p =
         in
         let ignore_list =
           List.filter sources ~f:(fun filename ->
-              String.length filename >= 9
-              && String.equal (String.sub filename ~pos:0 ~len:9) "/builtin/")
+              String.is_prefix ~prefix:"/builtin/" filename)
         in
         let sm_mappings = Source_map.Mappings.decode sm.mappings in
         let relocate pos m =