Enable the -Wundef warning for clang

webrtc/modules/audio_processing/gain_control_unittest.cc

 /*
  *  Copyright (c) 2016 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 <vector>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/base/array_view.h"
 #include "webrtc/modules/audio_processing/audio_buffer.h"
 #include "webrtc/modules/audio_processing/gain_control_impl.h"
 #include "webrtc/modules/audio_processing/test/audio_buffer_tools.h"
 #include "webrtc/modules/audio_processing/test/bitexactness_tools.h"
 
 namespace webrtc {
 namespace {
 
 const int kNumFramesToProcess = 100;
@@ skipping 407 matching lines @@
      DISABLED_Mono16kHz_AdaptiveDigital_Tl10_SL100_CG30_Lim_AL0_100) {
 #endif
   const int kStreamAnalogLevelReference = 100;
   const float kOutputReference[] = {-0.006134f, -0.004303f, -0.002716f};
   RunBitExactnessTest(16000, 1, GainControl::Mode::kAdaptiveDigital, 10, 100,
                       30, true, 0, 100, kStreamAnalogLevelReference,
                       kOutputReference);
 }
 
 }  // namespace webrtc