Fix MinGW-w64 GCC 4.7 compilation

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 246 matching lines @@
   __ call(ic, RelocInfo::CODE_TARGET);
   __ nop();
   __ nop();
 
   __ jmp(&L1);
   __ jmp(Operand(rbx, rcx, times_4, 10000));
 #ifdef ENABLE_DEBUGGER_SUPPORT
   ExternalReference after_break_target =
       ExternalReference(Debug_Address::AfterBreakTarget(),
                         assm.isolate());
+  USE(after_break_target);
 #endif  // ENABLE_DEBUGGER_SUPPORT
   __ jmp(ic, RelocInfo::CODE_TARGET);
   __ nop();
 
 
   Label Ljcc;
   __ nop();
   // long jumps
   __ j(overflow, &Ljcc);
   __ j(no_overflow, &Ljcc);
@@ skipping 143 matching lines @@
   CHECK(code->IsCode());
 #ifdef OBJECT_PRINT
   Code::cast(code)->Print();
   byte* begin = Code::cast(code)->instruction_start();
   byte* end = begin + Code::cast(code)->instruction_size();
   disasm::Disassembler::Disassemble(stdout, begin, end);
 #endif
 }
 
 #undef __