use int instead of long for ptrdiff_t on all 32-bit archs

use int instead of long for ptrdiff_t on all 32-bit archs

this is needed to match the underlying "ABI" standards. it's not
really an ABI issue since the binary representations are the same, but
having the wrong type can lead to errors when the type arising from a
difference-of-pointers expression does not match the defined type of
ptrdiff_t. most of the problems affect C++, not C.