Enable the -Wundef warning for clang

webrtc/modules/rtp_rtcp/source/vp8_partition_aggregator_unittest.cc

 /*
  *  Copyright (c) 2011 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 <stdlib.h>  // NULL
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/rtp_rtcp/source/vp8_partition_aggregator.h"
 
 namespace webrtc {
 
 TEST(PartitionTreeNode, CreateAndDelete) {
   const size_t kVector[] = {1, 2, 3};
   const size_t kNumPartitions = GTEST_ARRAY_SIZE_(kVector);
   PartitionTreeNode* node1 =
       PartitionTreeNode::CreateRootNode(kVector, kNumPartitions);
   PartitionTreeNode* node2 =
@@ skipping 179 matching lines @@
                 1600, kMTU, 1, 300, 900));
   EXPECT_EQ(3u,
             Vp8PartitionAggregator::CalcNumberOfFragments(
                 1600, kMTU, 1, 300, 798));
   EXPECT_EQ(2u,
             Vp8PartitionAggregator::CalcNumberOfFragments(
                 1600, kMTU, 1, 900, 1000));
 }
 
 }  // namespace webrtc