make buildworld: build changes only?

[Geert Hendrickx]

Hi, 

I'm keeping track of -STABLE on semi-regular basis.  But when I cvsup to
the latest sources and do make buildworld, it always starts to rebuild
the world entirely from scratch.  That's somewhat frustrating,
especially if cvsup showed only a screenful of changes.  

Is it possible to rebuild these changes only?  I know I could cd to the
directory of each changed file and do a make install there, but that is
of course not quite practical.  I suppose this could be automated, since
this was exactly the design principle of make: rebuild changed sources
only.  

I know this might brake some dependencies in some cases, but I expect
this to be rare.  I could still do a "full" buildworld when necessary.  

Any suggestions?  

GH