MFC r202964:

On FreeBSD, time_t is 64-bit for all platforms except i386 and powerpc,
where the type is 32-bit. ZFS can handle 64-bit timestamp internally
but zfs_setattr() would check if the time value can fit, we change the
checking macros to match 64-bit timestamp if the platform supports it.

This change has some downsides like, while you can import zfs on 32-bit
platforms, the timestamp would overflow if they are out of the range.

This fixes the Y2.038K issue on platforms using 64-bit timestamps.

Reviewed by: pjd