Port lib/libc/gen/t_siginfo to FreeBSD

- mcontext_t on FreeBSD doesn't have a __gregs field (it's split out on FreeBSD
into separate fields). In order to avoid muddying the test code with MD code,
the debugging trace info has not been implemented
- FreeBSD does not implement the si_stime and si_utime fields in siginfo_t, so
omit the debugging code that dumps the values
- sys/inttypes.h doesn't exist on FreeBSD

Sponsored by: EMC / Isilon Storage Division
libutil.h is required for fparseln on FreeBSD

Sponsored by: EMC / Isilon Storage Division
Add missing #include for sys/stat.h for fchmod

Sponsored by: EMC / Isilon Storage Division
it is not cast to a pointer of the specified type, it is cast to the
specified type...

mtod(m, uint8_t) does not work, mtod(m, uint8_t *) does work..
Port t_write to FreeBSD

- Mark the signo variable for the signal handle __unused
- Use limits.h instead of sys/syslimits.h (the latter does not
exist on FreeBSD)

Sponsored by: EMC / Isilon Storage Division
ixl: remove i40e_register_x710_int.h

This file is not used by the FreeBSD ixl driver.

Submitted by:	Eric Joyner <eric.joyner@intel.com>
MFC after:	3 days
Mark osi __unused so this compiles cleanly on FreeBSD

Sponsored by: EMC / Isilon Storage Division
unlink("/") fails with EISDIR instead of EBUSY on FreeBSD; test for that
instead

Sponsored by: EMC / Isilon Storage Division
Port t_chroot to FreeBSD

- Add missing #include sys/stat.h for mkdir(2)
- Omit the fchroot(2) tests because the support is not present on FreeBSD

Sponsored by: EMC / Isilon Storage Division