Enable the -Wundef warning for clang

webrtc/modules/audio_coding/neteq/test/RTPtimeshift.cc

 /*
  *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #include <stdio.h>
 #include <algorithm>
 #include <vector>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/audio_coding/neteq/test/NETEQTEST_RTPpacket.h"
 
 #define FIRSTLINELEN 40
 
 int main(int argc, char* argv[]) {
   if (argc < 4 || argc > 6) {
     printf(
         "Usage: RTPtimeshift in.rtp out.rtp newStartTS [newStartSN "
         "[newStartArrTime]]\n");
     exit(1);
@@ skipping 51 matching lines @@
     packet.writeToFile(outFile);
 
     packLen = packet.readFromFile(inFile);
   }
 
   fclose(inFile);
   fclose(outFile);
 
   return 0;
 }