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

src/frames.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 353 matching lines @@
   }
 }
 
 
 Code* StackFrame::GetSafepointData(Isolate* isolate,
                                    Address pc,
                                    SafepointEntry* safepoint_entry,
                                    unsigned* stack_slots) {
   PcToCodeCache::PcToCodeCacheEntry* entry =
       isolate->pc_to_code_cache()->GetCacheEntry(pc);
-  SafepointEntry cached_safepoint_entry = entry->safepoint_entry;
   if (!entry->safepoint_entry.is_valid()) {
     entry->safepoint_entry = entry->code->GetSafepointEntry(pc);
     ASSERT(entry->safepoint_entry.is_valid());
   } else {
     ASSERT(entry->safepoint_entry.Equals(entry->code->GetSafepointEntry(pc)));
   }
 
   // Fill in the results and return the code.
   Code* code = entry->code;
   *safepoint_entry = entry->safepoint_entry;
@@ skipping 886 matching lines @@
   ZoneList<StackFrame*> list(10);
   for (StackFrameIterator it; !it.done(); it.Advance()) {
     StackFrame* frame = AllocateFrameCopy(it.frame());
     list.Add(frame);
   }
   return list.ToVector();
 }
 
 
 } }  // namespace v8::internal