fix -Wunused-but-set-variable for gcc-4.6 on x64

src/x64/lithium-codegen-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 1865 matching lines @@
                                                 Label* map_check) {
   {
     PushSafepointRegistersScope scope(this);
     InstanceofStub::Flags flags = static_cast<InstanceofStub::Flags>(
         InstanceofStub::kNoFlags | InstanceofStub::kCallSiteInlineCheck);
     InstanceofStub stub(flags);
 
     __ push(ToRegister(instr->InputAt(0)));
     __ Push(instr->function());
 
-    Register temp = ToRegister(instr->TempAt(0));
     static const int kAdditionalDelta = 10;
     int delta =
         masm_->SizeOfCodeGeneratedSince(map_check) + kAdditionalDelta;
     ASSERT(delta >= 0);
     __ push_imm32(delta);
 
     // We are pushing three values on the stack but recording a
     // safepoint with two arguments because stub is going to
     // remove the third argument from the stack before jumping
     // to instanceof builtin on the slow path.
@@ skipping 2163 matching lines @@
   RegisterEnvironmentForDeoptimization(environment);
   ASSERT(osr_pc_offset_ == -1);
   osr_pc_offset_ = masm()->pc_offset();
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64