Enable the -Wundef warning for clang

webrtc/modules/audio_coding/neteq/audio_multi_vector_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_coding/neteq/audio_multi_vector.h"
 
 #include <assert.h>
 #include <stdlib.h>
 
 #include <string>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/typedefs.h"
 
 namespace webrtc {
 
 // This is a value-parameterized test. The test cases are instantiated with
 // different values for the test parameter, which is used to determine the
 // number of channels in the AudioMultiBuffer. Note that it is not possible
 // to combine typed testing with value-parameterized testing, and since the
 // tests for AudioVector already covers a number of different type parameters,
 // this test focuses on testing different number of channels, and keeping the
@@ skipping 285 matching lines @@
     EXPECT_EQ(vec[0][i], vec[num_channels_ - 1][i]);
   }
 }
 
 INSTANTIATE_TEST_CASE_P(TestNumChannels,
                         AudioMultiVectorTest,
                         ::testing::Values(static_cast<size_t>(1),
                                           static_cast<size_t>(2),
                                           static_cast<size_t>(5)));
 }  // namespace webrtc