Enable the -Wundef warning for clang

webrtc/modules/audio_processing/transient/wpd_node_unittest.cc

 /*
  *  Copyright (c) 2013 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_processing/transient/wpd_node.h"
 
 #include <string.h>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 namespace webrtc {
 
 static const size_t kDataLength = 5;
 static const float kTolerance = 0.0001f;
 
 static const size_t kParentDataLength = kDataLength * 2;
 static const float kParentData[kParentDataLength] =
     {1.f, 2.f, 3.f, 4.f, 5.f, 6.f, 7.f, 8.f, 9.f, 10.f};
 
@@ skipping 30 matching lines @@
 
 TEST(WPDNodeTest, ExpectedErrorReturnValue) {
   WPDNode node(kDataLength, kCoefficients, kCoefficientsLength);
   EXPECT_EQ(-1, node.Update(kParentData, kParentDataLength - 1));
   EXPECT_EQ(-1, node.Update(NULL, kParentDataLength));
   EXPECT_EQ(-1, node.set_data(kParentData, kDataLength - 1));
   EXPECT_EQ(-1, node.set_data(NULL, kDataLength));
 }
 
 }  // namespace webrtc