Since we've been making heavy use of unifdef recently: update it to the

Since we've been making heavy use of unifdef recently: update it to the
recent 2.10 release.

"This code was derived from software contributed to Berkeley by Dave Yost.
It was rewritten to support ANSI C by Tony Finch. The original version
of unifdef carried the 4-clause BSD copyright licence. None of its code
remains in this version (though some of the names remain) so it now
carries a more liberal licence."

ok deraadt@