Update WARN_UNUSED_RESULT macro to match Chromium's version.

webrtc/typedefs.h

 /*
  *  Copyright (c) 2012 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 50 matching lines @@
     defined(WEBRTC_DETECT_NEON)
 #define WEBRTC_CPU_DETECTION
 #endif
 
 // TODO(pbos): Use webrtc/base/basictypes.h instead to include fixed-size ints.
 #include <stdint.h>
 
 // Annotate a function indicating the caller must examine the return value.
 // Use like:
 //   int foo() WARN_UNUSED_RESULT;
+// To explicitly ignore a result, see |ignore_result()| in <base/macros.h>.
 // TODO(ajm): Hack to avoid multiple definitions until the base/ of webrtc and
 // libjingle are merged.
 #if !defined(WARN_UNUSED_RESULT)
-#if defined(__GNUC__)
+#if defined(__GNUC__) || defined(__clang__)
 #define WARN_UNUSED_RESULT __attribute__((warn_unused_result))
 #else
 #define WARN_UNUSED_RESULT
 #endif
 #endif  // WARN_UNUSED_RESULT
 
 // Put after a variable that might not be used, to prevent compiler warnings:
 //   int result ATTRIBUTE_UNUSED = DoSomething();
 //   assert(result == 17);
 #ifndef ATTRIBUTE_UNUSED
@@ skipping 17 matching lines @@
 // Annotate a function that will not return control flow to the caller.
 #if defined(_MSC_VER)
 #define NO_RETURN __declspec(noreturn)
 #elif defined(__GNUC__)
 #define NO_RETURN __attribute__((noreturn))
 #else
 #define NO_RETURN
 #endif
 
 #endif  // WEBRTC_TYPEDEFS_H_