> > There are currently only two things that *have* to be updated in the
> > running system during a build:
> > 
> > * /usr/share/mk

It seems to me that this could be fixed with a -I in things like
bsd.subdir.mak if DESTDIR is set (make would need to be modified
to honor the include path for sys.mk for this to really work though, but
that wouldn't be too hard).  You could hack around this by doing
something like:
	
 make -r -I${DESTDIR}/usr/share/mk -f ${DESTDIR}/usr/share/mk/sys.mk <makefile>

> > * /usr/share/tmac
> > 
> > Everything else should use the files in $DESTDIR if it's set.
> 
> actually, if you're willing to punt on the man pages (i.e. do a make
> with NOMAN= set), then you shouldn't need the latter...  8-)

Again, this could be fixed with a -M${DESTDIR}/usr/share/tmac in
bsd.man.mk, no?

You'd still have to do a make install with DESTDIR for
the make includes and the tmac files, but then it would work.
--
Mark