Fix unused variable warnings.

test/cctest/test-disasm-x64.cc

 // Copyright 2011 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 415 matching lines @@
   for (int i = 0; i < 16; i++) {
     __ Nop(i);
   }
 
   __ ret(0);
 
   CodeDesc desc;
   assm.GetCode(&desc);
   Handle<Code> code = isolate->factory()->NewCode(
       desc, Code::ComputeFlags(Code::STUB), Handle<Code>());
+  USE(code);
 #ifdef OBJECT_PRINT
   code->Print();
   byte* begin = code->instruction_start();
   byte* end = begin + code->instruction_size();
   disasm::Disassembler::Disassemble(stdout, begin, end);
 #endif
 }
 
 #undef __