ninja&make/mac: Only pass -x for loadable_modules.

test/mac/strip/file.c

 // Copyright (c) 2011 Google Inc. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 static void the_static_function() {}
+__attribute__((used)) void the_used_function() {}
+
+__attribute__((visibility("hidden"))) __attribute__((used))
+void the_hidden_function() {}
+__attribute__((visibility("default"))) __attribute__((used))
+void the_visible_function() {}
 
 void the_function() {
   the_static_function();
+  the_used_function();
+  the_hidden_function();
+  the_visible_function();
 }