Enable the -Wundef warning for clang

webrtc/modules/audio_processing/echo_cancellation_impl_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 <memory>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/audio_processing/aec/aec_core.h"
 #include "webrtc/modules/audio_processing/include/audio_processing.h"
 
 namespace webrtc {
 
 TEST(EchoCancellationInternalTest, ExtendedFilter) {
   std::unique_ptr<AudioProcessing> ap(AudioProcessing::Create());
   EXPECT_TRUE(ap->echo_cancellation()->aec_core() == NULL);
 
   EXPECT_EQ(ap->kNoError, ap->echo_cancellation()->Enable(true));
@@ skipping 46 matching lines @@
   config.Set<DelayAgnostic>(new DelayAgnostic(false));
   ap->SetExtraOptions(config);
   EXPECT_EQ(0, WebRtcAec_delay_agnostic_enabled(aec_core));
 
   // Retains setting after initialization.
   EXPECT_EQ(ap->kNoError, ap->Initialize());
   EXPECT_EQ(0, WebRtcAec_delay_agnostic_enabled(aec_core));
 }
 
 }  // namespace webrtc