Enable the -Wundef warning for clang

webrtc/modules/audio_coding/codecs/cng/cng_unittest.cc

 /*
  *  Copyright (c) 2011 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 <memory>
 #include <string>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/test/testsupport/fileutils.h"
 #include "webrtc/modules/audio_coding/codecs/cng/webrtc_cng.h"
 
 namespace webrtc {
 
 enum {
   kSidShortIntervalUpdate = 1,
   kSidNormalIntervalUpdate = 100,
   kSidLongIntervalUpdate = 10000
 };
@@ skipping 208 matching lines @@
       rtc::ArrayView<const int16_t>(speech_data_, 160), kNoSid, &sid_data));
 
   // Normal Encode, 100 msec, SID data should be generated all the time.
   for (int i = 0; i < 10; i++) {
     EXPECT_EQ(kCNGNumParamsNormal + 1, cng_encoder.Encode(
         rtc::ArrayView<const int16_t>(speech_data_, 160), kNoSid, &sid_data));
   }
 }
 
 }  // namespace webrtc