Enable the -Wundef warning for clang

webrtc/voice_engine/test/cmd_test/voe_cmd_test.cc

 /*
  *  Copyright (c) 2012 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 <stdlib.h>
 #include <string.h>
 #ifndef _WIN32
 #include <unistd.h>
 #endif
 
 #include <memory>
 #include <vector>
 
 #include "gflags/gflags.h"
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/base/format_macros.h"
 #include "webrtc/engine_configurations.h"
 #include "webrtc/modules/audio_processing/include/audio_processing.h"
 #include "webrtc/voice_engine/test/channel_transport/channel_transport.h"
 #include "webrtc/test/testsupport/fileutils.h"
 #include "webrtc/test/testsupport/trace_to_stderr.h"
 #include "webrtc/voice_engine/include/voe_audio_processing.h"
 #include "webrtc/voice_engine/include/voe_base.h"
 #include "webrtc/voice_engine/include/voe_codec.h"
 #include "webrtc/voice_engine/include/voe_errors.h"
@@ skipping 792 matching lines @@
 
   printf("Delete channels \n");
   res = base1->DeleteChannel(chan);
   VALIDATE;
 
   for (int i = 0; i < kMaxNumChannels; ++i) {
     res = base1->DeleteChannel(channels[i]);
     VALIDATE;
   }
 }