sysutils/nut: Build nut-scanner(8)

Depend on devel/ltdl and ensure that ${LOCALBASE}/include and
${LOCALBASE}/lib are available for ./configure to detect ltdl.h and
libltdl to facilitate building nut-scanner(8).

PR: 259153
Reported by: emaste

(cherry picked from commit 75ca0c0a1067e17e31335a0cd1c85e2432d9e51a)