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

src/x64/full-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 4042 matching lines @@
       PrepareForBailoutBeforeSplit(TOS_REG, true, if_true, if_false);
       __ testq(rax, rax);
        // The stub returns 0 for true.
       Split(zero, if_true, if_false, fall_through);
       break;
     }
 
     default: {
       VisitForAccumulatorValue(expr->right());
       Condition cc = no_condition;
-      bool strict = false;
       switch (op) {
         case Token::EQ_STRICT:
-          strict = true;
           // Fall through.
         case Token::EQ:
           cc = equal;
           __ pop(rdx);
           break;
         case Token::LT:
           cc = less;
           __ pop(rdx);
           break;
         case Token::GT:
@@ skipping 154 matching lines @@
   __ jmp(rdx);
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64