find: Re-enable the -acl primary on FreeBSD

This was made conditional to support cross-builds, but the relevant
header wasn't included so it was never enabled for native builds.

PR: 278124
Fixes: c3a6ea5ba6b5 Allow compiling usr.bin/find on Linux and Mac
(cherry picked from commit 984add354edef8a6b4983a33f89ff62532a1556b)