Can you try it as an unprivileged user? There's a check for /dev/tun0 which is never going to be relevant to cross-compiling.
libdnet build on FreeBSD is broken, unprivileged user
freebsd: do not build as root
libdnet: fix for FreeBSD /dev/tun0
Did 24caa58 work?
Works for me at 9537e5c