Enable the -Wundef warning for clang

webrtc/modules/audio_processing/beamformer/matrix_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 <complex>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/audio_processing/beamformer/matrix.h"
 #include "webrtc/modules/audio_processing/beamformer/matrix_test_helpers.h"
 
 namespace webrtc {
 
 using std::complex;
 
 TEST(MatrixTest, TestMultiplySameSize) {
   const int kNumRows = 2;
   const int kNumCols = 2;
@@ skipping 293 matching lines @@
   actual_result_multiply.Multiply(lh_mat, rh_mat);
   MatrixTestHelpers::ValidateMatrixEqualityComplexFloat(
       expected_result_multiply, actual_result_multiply);
 
   actual_result_pointwise_divide.PointwiseDivide(lh_mat, rh_mat);
   MatrixTestHelpers::ValidateMatrixEqualityComplexFloat(
       expected_result_pointwise_divide, actual_result_pointwise_divide);
 }
 
 }  // namespace webrtc