Enable the -Wundef warning for clang

webrtc/modules/audio_coding/neteq/buffer_level_filter_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.
  */
 
 // Unit tests for BufferLevelFilter class.
 
 #include "webrtc/modules/audio_coding/neteq/buffer_level_filter.h"
 
 #include <math.h>  // Access to pow function.
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 namespace webrtc {
 
 TEST(BufferLevelFilter, CreateAndDestroy) {
   BufferLevelFilter* filter = new BufferLevelFilter();
   EXPECT_EQ(0, filter->filtered_current_level());
   delete filter;
 }
 
 TEST(BufferLevelFilter, ConvergenceTest) {
@@ skipping 125 matching lines @@
   filter.Update(filter.filtered_current_level() >> 8, kTimeStretchedSamples,
                 kPacketSizeSamples);
   EXPECT_EQ(21, filter.filtered_current_level() >> 8);
   // Try negative value and verify that we come back to the previous result.
   filter.Update(filter.filtered_current_level() >> 8, -kTimeStretchedSamples,
                 kPacketSizeSamples);
   EXPECT_EQ(kExpectedValue, filter.filtered_current_level() >> 8);
 }
 
 }  // namespace webrtc