Enable the -Wundef warning for clang

webrtc/common_audio/wav_file_unittest.cc

 /*
  *  Copyright (c) 2014 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.
  */
 
 // MSVC++ requires this to be set before any other includes to get M_PI.
 #define _USE_MATH_DEFINES
 
 #include <cmath>
 #include <limits>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/common_audio/wav_header.h"
 #include "webrtc/common_audio/wav_file.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 namespace webrtc {
 
 static const float kSamples[] = {0.0, 10.0, 4e4, -1e9};
 
 // Write a tiny WAV file with the C++ interface and verify the result.
 TEST(WavWriterTest, CPP) {
@@ skipping 140 matching lines @@
     float read_samples[kNumSamples];
     EXPECT_EQ(kNumSamples, r.ReadSamples(kNumSamples, read_samples));
     for (size_t i = 0; i < kNumSamples; ++i)
       EXPECT_NEAR(samples[i], read_samples[i], 1);
 
     EXPECT_EQ(0u, r.ReadSamples(kNumSamples, read_samples));
   }
 }
 
 }  // namespace webrtc