Enable the -Wundef warning for clang

webrtc/modules/audio_processing/transient/transient_suppressor_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.
  */
 
 #include "webrtc/modules/audio_processing/transient/transient_suppressor.h"
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/audio_processing/transient/common.h"
 
 namespace webrtc {
 
 TEST(TransientSuppressorTest, TypingDetectionLogicWorksAsExpectedForMono) {
   static const int kNumChannels = 1;
 
   TransientSuppressor ts;
   ts.Initialize(ts::kSampleRate16kHz, ts::kSampleRate16kHz, kNumChannels);
 
@@ skipping 52 matching lines @@
     EXPECT_TRUE(ts.suppression_enabled_);
   }
   for (int time_ms = 0; time_ms < 1000; time_ms += ts::kChunkSizeMs) {
     ts.UpdateKeypress(false);
     EXPECT_FALSE(ts.detection_enabled_);
     EXPECT_FALSE(ts.suppression_enabled_);
   }
 }
 
 }  // namespace webrtc