Fix gcc error for ignoring return value on stack_trace_posix.cc

src/base/debug/stack_trace_posix.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Slightly adapted for inclusion in V8.
 // Copyright 2016 the V8 project authors. All rights reserved.
 
 #include "src/base/debug/stack_trace.h"
 
 #include <errno.h>
@@ skipping 157 matching lines @@
       handler->HandleOutput(" [");
       OutputPointer(trace[i], handler);
       handler->HandleOutput("]\n");
     }
   }
 }
 
 void PrintToStderr(const char* output) {
   // NOTE: This code MUST be async-signal safe (it's used by in-process
   // stack dumping signal handler). NO malloc or stdio is allowed here.
-  write(STDERR_FILENO, output, strlen(output));
+  ssize_t return_val = write(STDERR_FILENO, output, strlen(output));
+  USE(return_val);
 }
 
 void StackDumpSignalHandler(int signal, siginfo_t* info, void* void_context) {
   // NOTE: This code MUST be async-signal safe.
   // NO malloc or stdio is allowed here.
 
   // Record the fact that we are in the signal handler now, so that the rest
   // of StackTrace can behave in an async-signal-safe manner.
   in_signal_handler = 1;
 
@@ skipping 247 matching lines @@
     *start++ = ch;
   }
   return buf;
 }
 
 }  // namespace internal
 
 }  // namespace debug
 }  // namespace base
 }  // namespace v8