Atomic::cmpxchg_ptr code duplication

[John Coomes]

The Atomic class has both

  intptr_t cmpxchg_ptr(intptr_t, volatile intptr_t*, intptr_t);
  void*    cmpxchg_ptr(void*, volatile void*, void*);

The latter could be implemented as a simple inline which calls the
former:

  void* cmpxchg_ptr(void* exchange_value, volatile void* dest,
                    void* compare_value) {
    return (intptr_t)cmpxchg_ptr((intptr_t)exchange_value,
                                 (volatile intptr_t*)dest,
                                 (intptr_t)compare_value
   }

However, both the intptr_t and void* variants have bodies defined in
each of the various platform-specific headers (e.g.,
atomic_windows_x86.inline.hpp, atomic_solaris_x86.inline.hpp, ...).
So there are 10 places where the cmpxchg_ptr(void*...) variant is
defined, instead of one.  Is there a reason for the duplication?

-John