Make WARN_UNUSED_RESULT a no-op on gcc

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 47 matching lines @@
 // TODO(zhongwei.yao): WEBRTC_CPU_DETECTION is only used in one place; we should
 // probably just remove it.
 #if (defined(WEBRTC_ARCH_X86_FAMILY) && !defined(__SSE2__))
 #define WEBRTC_CPU_DETECTION
 #endif
 
 #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__) || defined(__clang__)
-#define WARN_UNUSED_RESULT __attribute__ ((__warn_unused_result__))
+//   int foo() RTC_WARN_UNUSED_RESULT;
+// To explicitly ignore a result, cast to void.
+// TODO(kwiberg): Remove when we can use [[nodiscard]] from C++17.
+#if defined(__clang__)
+#define RTC_WARN_UNUSED_RESULT __attribute__((__warn_unused_result__))
+#elif defined(__GNUC__)
+// gcc has a __warn_unused_result__ attribute, but you can't quiet it by
+// casting to void, so we don't use it.
+#define RTC_WARN_UNUSED_RESULT
 #else
-#define WARN_UNUSED_RESULT
+#define RTC_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);
 // Deprecated since it only works with GCC & clang. See RTC_UNUSED below.
 // TODO(terelius): Remove.
 #ifndef ATTRIBUTE_UNUSED
 #if defined(__GNUC__) || defined(__clang__)
 #define ATTRIBUTE_UNUSED __attribute__ ((__unused__))
 #else
@@ skipping 26 matching lines @@
 //   int result = DoSomething();
 //   assert(result == 17);
 //   RTC_UNUSED(result);
 // Note: In most cases it is better to remove the unused variable rather than
 // suppressing the compiler warning.
 #ifndef RTC_UNUSED
 #define RTC_UNUSED(x) static_cast<void>(x)
 #endif  // RTC_UNUSED
 
 #endif  // WEBRTC_TYPEDEFS_H_