Enable the -Wundef warning for clang

webrtc/modules/video_coding/utility/simulcast_rate_allocator_unittest.cc

 /*
  *  Copyright (c) 2016 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/video_coding/utility/simulcast_rate_allocator.h"
 
 #include <limits>
 #include <memory>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 namespace webrtc {
 namespace {
 constexpr uint32_t kMinBitrate = 50;
 constexpr uint32_t kTargetBitrate = 100;
 constexpr uint32_t kMaxBitrate = 1000;
 }  // namespace
 
 class SimulcastRateAllocatorTest : public ::testing::Test {
  public:
@@ skipping 175 matching lines @@
                              codec_.simulcastStream[1].targetBitrate +
                              codec_.simulcastStream[2].maxBitrate;
     uint32_t expected[] = {codec_.simulcastStream[0].targetBitrate,
                            codec_.simulcastStream[1].targetBitrate,
                            codec_.simulcastStream[2].maxBitrate};
     ExpectEqual(expected, allocator_->GetAllocation(bitrate));
   }
 }
 
 }  // namespace webrtc