Populating /usr/include for make buildworld?

Hi,

I am trying to see if I have any outdated files in /usr/include by
doing:
cd /usr/obj ; rm -r *
cd /usr/include ; rm -r *
cd /usr/src; make buildworld

buildworld is failing in a few places because
the installincludes step is not populating
/usr/include/zlib.h, /usr/include/zconf.h, or /usr/include/termcap.h

What is the correct way to populate /usr/include 
before buildworld?

Thanks.

-- 
Craig Rodrigues        
rodrigc_at_crodrigues.org