Enable the -Wundef warning for clang

NOPRESUBMIT=true
BUG=webrtc:6398

Review-Url: https://codereview.webrtc.org/2358993004
Cr-Original-Commit-Position: refs/heads/master@{#14425}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 77eab704707e03c74eda3126b92e4ef5e2b7eb4d
diff --git a/common_audio/real_fourier_unittest.cc b/common_audio/real_fourier_unittest.cc
index 367fec3..dab28bb 100644
--- a/common_audio/real_fourier_unittest.cc
+++ b/common_audio/real_fourier_unittest.cc
@@ -12,7 +12,7 @@
 
 #include <stdlib.h>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/common_audio/real_fourier_openmax.h"
 #include "webrtc/common_audio/real_fourier_ooura.h"