Enable the -Wundef warning for clang

webrtc/common_audio/vad/vad_filterbank_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 <stdlib.h>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/common_audio/vad/vad_unittest.h"
 #include "webrtc/typedefs.h"
 
 extern "C" {
 #include "webrtc/common_audio/vad/vad_core.h"
 #include "webrtc/common_audio/vad/vad_filterbank.h"
 }
 
 namespace {
 
@@ skipping 59 matching lines @@
                                                features));
       for (int k = 0; k < kNumChannels; ++k) {
         EXPECT_EQ(kOffsetVector[k], features[k]);
       }
     }
   }
 
   free(self);
 }
 }  // namespace