Enable the -Wundef warning for clang

webrtc/common_audio/vad/vad_gmm_unittest.cc

 /*
  *  Copyright (c) 2011 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 "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_gmm.h"
 }
 
 namespace {
 
 TEST_F(VadTest, vad_gmm) {
@@ skipping 12 matching lines @@
   EXPECT_EQ(1024, WebRtcVad_GaussianProbability(75, 128, 128, &delta));
   EXPECT_EQ(7552, delta);
   EXPECT_EQ(1024, WebRtcVad_GaussianProbability(-75, -128, 128, &delta));
   EXPECT_EQ(-7552, delta);
 
   // Too large input, should give zero probability.
   EXPECT_EQ(0, WebRtcVad_GaussianProbability(105, 0, 128, &delta));
   EXPECT_EQ(13440, delta);
 }
 }  // namespace