Enable the -Wundef warning for clang

webrtc/modules/audio_processing/transient/transient_detector_unittest.cc

 /*
  *  Copyright (c) 2013 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_processing/transient/transient_detector.h"
 
 #include <memory>
 #include <sstream>
 #include <string>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/audio_processing/transient/common.h"
 #include "webrtc/modules/audio_processing/transient/file_utils.h"
 #include "webrtc/system_wrappers/include/file_wrapper.h"
 #include "webrtc/test/testsupport/fileutils.h"
 #include "webrtc/typedefs.h"
 
 namespace webrtc {
 
 static const int kSampleRatesHz[] = {ts::kSampleRate8kHz,
                                      ts::kSampleRate16kHz,
@@ skipping 67 matching lines @@
       EXPECT_NEAR(file_value, detector_value, kTolerance) << "Frame: "
           << frames_read;
     }
 
     detect_file->CloseFile();
     audio_file->CloseFile();
   }
 }
 
 }  // namespace webrtc