flambda-backend: Fix a bug with warning 199 and -stop-after typing (#2513)

Author: ccasin

driver/compile_common.ml

@@ -139,9 +139,10 @@ let implementation ~hook_parse_tree ~hook_typed_tree info ~backend =
       let typed = typecheck_impl info parsed in
       hook_typed_tree typed;
       if Clflags.(should_stop_after Compiler_pass.Typing) then () else begin
-        backend info typed
+        backend info typed;
       end;
     end;
-    Builtin_attributes.warn_unchecked_property ();
+    if not (Clflags.(should_stop_after Compiler_pass.Selection)) then
+      Builtin_attributes.warn_unchecked_property ();
     Warnings.check_fatal ();
   )