Do not use __ptr_t

[Paul Eggert]

Thanks, that patch looks good as far as it goes. How about deprecating __ptr_t 
while we're at it? Although we can't deprecate a macro directly, we can do this:

typedef void __ptr_t_void __attribute_deprecated__;
/* This is not a typedef so 'const __ptr_t' does the right thing.  */
#define __ptr_t __ptr_t_void *