Enable the -Wundef warning for clang

webrtc/modules/audio_coding/neteq/dtmf_tone_generator_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.
  */
 
 // Unit tests for DtmfToneGenerator class.
 
 #include "webrtc/modules/audio_coding/neteq/dtmf_tone_generator.h"
 
 #include <math.h>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/audio_coding/neteq/audio_multi_vector.h"
 
 namespace webrtc {
 
 class DtmfToneGeneratorTest : public ::testing::Test {
  protected:
   static const double kLowFreqHz[16];
   static const double kHighFreqHz[16];
   // This is the attenuation applied to all cases.
   const double kBaseAttenuation = 16141.0 / 16384.0;
@@ skipping 142 matching lines @@
 
   // Initialize with valid parameters.
   ASSERT_EQ(0, tone_gen.Init(fs, event, attenuation));
   EXPECT_TRUE(tone_gen.initialized());
   // NULL pointer to destination.
   EXPECT_EQ(DtmfToneGenerator::kParameterError,
             tone_gen.Generate(kNumSamples, NULL));
 }
 
 }  // namespace webrtc