Enable the -Wundef warning for clang

webrtc/common_audio/vad/vad_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/common_audio/vad/vad_unittest.h"
 
 #include <stdlib.h>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 #include "webrtc/base/arraysize.h"
 #include "webrtc/base/checks.h"
 #include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
 #include "webrtc/common_audio/vad/include/webrtc_vad.h"
 #include "webrtc/typedefs.h"
 
 VadTest::VadTest() {}
 
 void VadTest::SetUp() {}
@@ skipping 121 matching lines @@
         EXPECT_EQ(-1, WebRtcVad_ValidRateAndFrameLength(kRates[i],
                                                         kFrameLengths[j]));
       }
     }
   }
 }
 
 // TODO(bjornv): Add a process test, run on file.
 
 }  // namespace