Fix the GC branch so it compiles and runs on 64 bit.

src/incremental-marking.h

 // 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 215 matching lines @@
   static void SetNewSpacePageFlags(MemoryChunk* chunk, bool is_marking);
 
   Heap* heap_;
 
   State state_;
   MarkingDeque marking_deque_;
 
   int steps_count_;
   double steps_took_;
   bool should_hurry_;
-  intptr_t allocation_marking_factor_;
+  int allocation_marking_factor_;
   intptr_t allocated_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_INCREMENTAL_MARKING_H_