Enable the -Wundef warning for clang

webrtc/modules/audio_coding/neteq/dtmf_buffer_unittest.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 "webrtc/modules/audio_coding/neteq/dtmf_buffer.h"
 
 #ifdef WIN32
 #include <winsock2.h>  // ntohl()
 #else
 #include <arpa/inet.h>  // ntohl()
 #endif
 
 #include <iostream>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 // Modify the tests so that they pass with the modifications done to DtmfBuffer
 // for backwards bit-exactness. Once bit-exactness is no longer required, this
 // #define should be removed (and the code that it enables).
 #define LEGACY_BITEXACT
 
 namespace webrtc {
 
 static int sample_rate_hz = 8000;
 
@@ skipping 260 matching lines @@
   event.duration = 0;
   EXPECT_EQ(DtmfBuffer::kInvalidEventParameters, buffer.InsertEvent(event));
   event.duration = 0xFFFF + 1;
   EXPECT_EQ(DtmfBuffer::kInvalidEventParameters, buffer.InsertEvent(event));
   event.duration = 1;  // Valid value;
 
   // Finish with a valid event, just to verify that all is ok.
   EXPECT_EQ(DtmfBuffer::kOK, buffer.InsertEvent(event));
 }
 }  // namespace webrtc