[arm64] Fix GCC build warnings.

src/arm64/builtins-arm64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_ARM64
 
 #include "src/arm64/frames-arm64.h"
 #include "src/codegen.h"
 #include "src/debug/debug.h"
 #include "src/deoptimizer.h"
@@ skipping 1183 matching lines @@
   //  -- x3 : new target (preserved for callee)
   //  -- x1 : target function (preserved for callee)
   // -----------------------------------
   // First lookup code, maybe we don't need to compile!
   Label gotta_call_runtime;
   Label maybe_call_runtime;
   Label try_shared;
   Label loop_top, loop_bottom;
 
   Register closure = x1;
-  Register new_target = x3;
   Register map = x13;
   Register index = x2;
   __ Ldr(map, FieldMemOperand(closure, JSFunction::kSharedFunctionInfoOffset));
   __ Ldr(map,
          FieldMemOperand(map, SharedFunctionInfo::kOptimizedCodeMapOffset));
   __ Ldrsw(index, UntagSmiFieldMemOperand(map, FixedArray::kLengthOffset));
   __ Cmp(index, Operand(2));
   __ B(lt, &gotta_call_runtime);
 
   // Find literals.
@@ skipping 1690 matching lines @@
   }
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM