Prior to building libabac you must install libstrongswan.

Download strongswan-4.4.0 from strongswan.org:
    http://download.strongswan.org/strongswan-4.4.0.tar.bz2

FreeBSD users: add --with-group=wheel to strongswan ./configure

$ tar xjvf strongswan-4.4.0.tar.bz2
$ cd strongswan-4.4.0
$ ./configure --enable-monolithic    [FreeBSD: see note above]
$ cd src/libstrongswan
$ make && sudo make install

Be sure to make note of the directory into which you've untarred
strongswan-4.4.0.tar.bz2. You will use this in the next step.

BUILDING LIBABAC

$ ./configure --with-strongswan=$STRONGSWAN_SRC_DIR
$ make && sudo make install