Enable the -Wundef warning for clang

webrtc/common_audio/lapped_transform_unittest.cc

 /*
  *  Copyright (c) 2014 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/common_audio/lapped_transform.h"
 
 #include <algorithm>
 #include <cmath>
 #include <cstring>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 using std::complex;
 
 namespace {
 
 class NoopCallback : public webrtc::LappedTransform::Callback {
  public:
   NoopCallback() : block_num_(0) {}
 
   virtual void ProcessAudioBlock(const complex<float>* const* in_block,
@@ skipping 171 matching lines @@
   {
     const size_t kExpectedChunkLength = 160;
     const LappedTransform trans(1, 1, kExpectedChunkLength, window,
                                 kBlockLength, kBlockLength, &call);
 
     EXPECT_EQ(kExpectedChunkLength, trans.chunk_length());
   }
 }
 
 }  // namespace webrtc