Use return value from fwrite in log.cc to please compilers.

src/log.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1360 matching lines @@
   LogMessageBuilder msg;
   msg.Append("code-info,%s,%d\n", arch, Code::kHeaderSize);
   msg.WriteToLogFile();
 #endif  // ENABLE_LOGGING_AND_PROFILING
 }
 
 
 void Logger::LowLevelCodeCreateEvent(Code* code, LogMessageBuilder* msg) {
   if (!FLAG_ll_prof || Log::output_code_handle_ == NULL) return;
   int pos = static_cast<int>(ftell(Log::output_code_handle_));
-  fwrite(code->instruction_start(), 1, code->instruction_size(),
-         Log::output_code_handle_);
+  int rv = fwrite(code->instruction_start(), 1, code->instruction_size(),
+                  Log::output_code_handle_);
+  ASSERT(static_cast<size_t>(code->instruction_size()) == rv);
+  USE(rv);
   msg->Append(",%d", pos);
 }
 
 
 void Logger::LogCodeObjects() {
   AssertNoAllocation no_alloc;
   HeapIterator iterator;
   for (HeapObject* obj = iterator.next(); obj != NULL; obj = iterator.next()) {
     if (obj->IsCode()) LogCodeObject(obj);
   }
@@ skipping 246 matching lines @@
   }
   // Otherwise, if the sliding state window computation has not been
   // started we do it now.
   if (sliding_state_window_ == NULL) {
     sliding_state_window_ = new SlidingStateWindow();
   }
 #endif
 }
 
 } }  // namespace v8::internal