Enable the -Wundef warning for clang

webrtc/audio/audio_state_unittest.cc

 /*
  *  Copyright (c) 2015 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 "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 #include "webrtc/audio/audio_state.h"
 #include "webrtc/test/mock_voice_engine.h"
 
 namespace webrtc {
 namespace test {
 namespace {
 
 struct ConfigHelper {
   ConfigHelper() {
@@ skipping 48 matching lines @@
   voe_observer->CallbackOnError(-1, VE_NOT_INITED);
   EXPECT_TRUE(audio_state->typing_noise_detected());
 
   voe_observer->CallbackOnError(-1, VE_TYPING_NOISE_OFF_WARNING);
   EXPECT_FALSE(audio_state->typing_noise_detected());
   voe_observer->CallbackOnError(-1, VE_NOT_INITED);
   EXPECT_FALSE(audio_state->typing_noise_detected());
 }
 }  // namespace test
 }  // namespace webrtc