Enable the -Wundef warning for clang

webrtc/modules/audio_processing/beamformer/covariance_matrix_generator_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.
  */
 
 #define _USE_MATH_DEFINES
 
 #include "webrtc/modules/audio_processing/beamformer/covariance_matrix_generator.h"
 
 #include <cmath>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/audio_processing/beamformer/matrix_test_helpers.h"
 
 namespace webrtc {
 
 using std::complex;
 
 TEST(CovarianceMatrixGeneratorTest, TestUniformCovarianceMatrix2Mics) {
   const float kWaveNumber = 0.5775f;
   const int kNumberMics = 2;
   const float kMicSpacing = 0.05f;
@@ skipping 193 matching lines @@
   EXPECT_NEAR(actual_els[1][2].imag(), 0.1546f, kTolerance);
   EXPECT_NEAR(actual_els[2][0].imag(), -0.274f, kTolerance);
   EXPECT_NEAR(actual_els[2][1].imag(), -0.1546f, kTolerance);
   EXPECT_NEAR(actual_els[2][2].imag(), 0.f, kTolerance);
 }
 
 // PhaseAlignmentMasks is tested by AngledCovarianceMatrix and by
 // InitBeamformerWeights in BeamformerUnittest.
 
 }  // namespace webrtc