Enable the -Wundef warning for clang

webrtc/modules/audio_processing/vad/standalone_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/modules/audio_processing/vad/standalone_vad.h"
 
 #include <string.h>
 
 #include <memory>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/include/module_common_types.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 namespace webrtc {
 
 TEST(StandaloneVadTest, Api) {
   std::unique_ptr<StandaloneVad> vad(StandaloneVad::Create());
   int16_t data[kLength10Ms] = {0};
 
   // Valid frame length (for 32 kHz rate), but not what the VAD is expecting.
@@ skipping 71 matching lines @@
         // When inactive, probabilities are set to 0.01.
         for (int n = 0; n < kNumVadFramesToProcess; n++)
           EXPECT_EQ(0.01, p[n]);
       }
     }
   }
   fclose(reference_file);
   fclose(pcm_file);
 }
 }  // namespace webrtc