Enable the -Wundef warning for clang

webrtc/modules/audio_coding/neteq/audio_vector_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/audio_vector.h"
 
 #include <assert.h>
 #include <stdlib.h>
 
 #include <string>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/typedefs.h"
 
 namespace webrtc {
 
 class AudioVectorTest : public ::testing::Test {
  protected:
   virtual void SetUp() {
     // Populate test array.
     for (size_t i = 0; i < array_length(); ++i) {
       array_[i] = i;
@@ skipping 348 matching lines @@
     EXPECT_NEAR((i + 1) * 100 / (kFadeLength + 1),
                 vec1[kLength - kFadeLength + i], 1);
   }
   // Second part untouched.
   for (size_t i = kLength; i < vec1.Size(); ++i) {
     EXPECT_EQ(100, vec1[i]);
   }
 }
 
 }  // namespace webrtc