sysconf: add a poudriere target

[dteske]

Summary

poudriere.conf is handed to sysrc(8), including the jail, tree, and
set overlays poudriere(8) consults. make, src, and src-env are
sub-targets over the matching make(1) files under poudriere.d. -l
and -L list one path per line; -L includes overlays that do not exist
yet. A bare -- ends the sub-target so the next word is a variable.
Bump sysconf(8) to 2.2.