Enable the -Wundef warning for clang

webrtc/voice_engine/voe_audio_processing_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/voice_engine/include/voe_audio_processing.h"
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/voice_engine/include/voe_base.h"
 
 namespace webrtc {
 namespace voe {
 namespace {
 
 class VoEAudioProcessingTest : public ::testing::Test {
  protected:
   VoEAudioProcessingTest()
       : voe_(VoiceEngine::Create()),
@@ skipping 33 matching lines @@
     EXPECT_EQ(-1, audioproc_->EnableDriftCompensation(true));
     EXPECT_FALSE(audioproc_->DriftCompensationEnabled());
     EXPECT_EQ(-1, audioproc_->EnableDriftCompensation(false));
     EXPECT_FALSE(audioproc_->DriftCompensationEnabled());
   }
 }
 
 }  // namespace
 }  // namespace voe
 }  // namespace webrtc