mmap64: always use unsigned 64bit offsets

mmap64: always use unsigned 64bit offsets

The current code will sometimes cast the offset to an unsigned long.
On 32bit systems, that doesn't make much sense since we always know
that the off64_t type is 64bits.  So drop the ifdef logic, cast it
to an unsigned 64bit value, and then do the shift.

If the system is 32bits, and the address is still too large, then
there's really nothing we could do about it anyways, so the extra
ifdef logic wasn't helping.

URL: https://bugs.busybox.net/show_bug.cgi?id=3853
Signed-off-by: Mike Frysinger <vapier@gentoo.org>