You need sljit (http://sljit.sourceforge.net/) and mk-configure (http://sourceforge.net/projects/mk-configure/) to build bpfjit.
It is recommended to use pkgsrc and install devel/mk-configure. The pkgsrc guide is available at http://www.netbsd.org/docs/pkgsrc/.
The sljit code must be at revision r220 or newer:
$ svn co https://sljit.svn.sourceforge.net/svnroot/sljit@r220 sljit
$ tar cf sljit-r220.tar sljit/
Extract sljit tarball to sljit/ subdirectory. Make sure you pass --keep-old-files (-k) option to tar to keep Makefiles from bpfjit.
$ cd sljit/
$ tar kxf /path/to/sljit-r220.tar
Then you can build bpfjit with this command
$ mkcmake
and install:
$ export DESTDIR=/path/of/your/choice
$ env PREFIX=/ mkcmake install
$ export LD_LIBRARY_PATH=${DESTDIR}/lib
$ cd ${DESTDIR}
$ ./bin/bpfjit_test
$ echo $?
You should see zero exit status.