I tried to build the FreeBSD HEAD kernel using the [debian kfreebsd-7] package (as described at [kfreebsd svn build]). It looks like FreeBSD HEAD needs the "p" option of the command "uudecode", that is not present in GNU sharutils version.
Take a look at kfreebsd-7/debian/patches/913_uudecode.diff It looks like it have to be extended for kfreebsd-8. Petr