function were put in i386/i386/machdep.c from where it has been
cut and pasted to other architectures with only minor corruption.
Disklabel is really a MI format in many ways, at least it certainly
is when you operate on struct disklabel.
Put bounds_check_with_label() back in subr_disklabel.c where it belongs.
Sponsored by: DARPA & NAI Labs.