Enable the -Wundef warning for clang

webrtc/base/bitbuffer_unittest.cc

 /*
  *  Copyright 2015 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.
  */
 
@@ skipping 150 matching lines @@
   EXPECT_EQ(4u, bit_offset);
   EXPECT_TRUE(buffer.Seek(4, 0));
   EXPECT_FALSE(buffer.Seek(5, 0));
   buffer.GetCurrentOffset(&byte_offset, &bit_offset);
   EXPECT_EQ(4u, byte_offset);
   EXPECT_EQ(0u, bit_offset);
   EXPECT_FALSE(buffer.Seek(4, 1));
 
   // Disable death test on Android because it relies on fork() and doesn't play
   // nicely.
-#if defined(GTEST_HAS_DEATH_TEST)
+#if GTEST_HAS_DEATH_TEST
 #if !defined(WEBRTC_ANDROID)
   // Passing a NULL out parameter is death.
   EXPECT_DEATH(buffer.GetCurrentOffset(&byte_offset, NULL), "");
 #endif
 #endif
 }
 
 uint64_t GolombEncoded(uint32_t val) {
   val++;
   uint32_t bit_counter = val;
@@ skipping 139 matching lines @@
   EXPECT_TRUE(buffer.WriteBits(0, 1));
   EXPECT_EQ(0xEFu, bytes[0]);
   EXPECT_TRUE(buffer.WriteBits(0, 3));
   EXPECT_EQ(0xE1u, bytes[0]);
   EXPECT_TRUE(buffer.WriteBits(0, 2));
   EXPECT_EQ(0xE0u, bytes[0]);
   EXPECT_EQ(0x7F, bytes[1]);
 }
 
 }  // namespace rtc