- Removed the redefination in the atomicword_compat.h. Now Atomic32 will
alwyas be intptr_t in 32bit platforms, the bridge is no longer needed.
- Change NaCl 64bit to use intptr_t instead of int32 for Atomic32,
otherwise AtmoicWord APIs will miss the definations.

After this change, the AtmoicWord will always be either Atomic32 or
Atmoic64 depending on the platforms.