Define special case for atf which libraries names are different from their
declaration


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274997 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Fix build.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274998 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Do not overwrite any LIBNETBSD or LIBNETBSDDIR if they are already defined


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274999 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f