Enable the -Wundef warning for clang

webrtc/modules/audio_processing/high_pass_filter_unittest.cc

 /*
  *  Copyright (c) 2015 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 <vector>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/base/array_view.h"
 #include "webrtc/modules/audio_processing/audio_buffer.h"
 #include "webrtc/modules/audio_processing/high_pass_filter_impl.h"
 #include "webrtc/modules/audio_processing/test/audio_buffer_tools.h"
 #include "webrtc/modules/audio_processing/test/bitexactness_tools.h"
 
 namespace webrtc {
 namespace {
 
 // Process one frame of data and produce the output.
@@ skipping 654 matching lines @@
       -0.816528f, 0.085421f,  0.739647f,  -0.922089f, 0.669301f,  -0.048187f,
       -0.290039f, -0.818085f, -0.596008f, -0.177826f, -0.002197f, -0.350647f,
       -0.064301f, 0.337291f,  -0.621765f, 0.115909f,  0.311899f,  -0.915924f,
       0.020478f,  0.836055f,  -0.714020f, -0.037140f, 0.391125f,  -0.340118f};
 
   RunBitexactnessTest(
       16000, 2, CreateVector(rtc::ArrayView<const float>(kReferenceInput)),
       CreateVector(rtc::ArrayView<const float>(kReference)));
 }
 }  // namespace webrtc