Make test/cxxflags use a user define instead of __OPTIMIZE__

test/cxxflags/cxxflags.cc

 /* Copyright (c) 2010 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. */
 
 #include <stdio.h>
 
 int main(int argc, char *argv[])
 {
-#ifdef __OPTIMIZE__
-  printf("Using an optimization flag\n");
+#ifdef ABC
+  printf("With define\n");
 #else
-  printf("Using no optimization flag\n");
+  printf("No define\n");
 #endif
   return 0;
 }