Log Message:
This probes for and uses libedit, but libedit isn't buildlinked.
Correct that optimistically by including (optimistically) readline.bl3.mk,
in the hopes that readline will work too. If not, someone should revisit
this and explicitly include devel/editline/bl3.mk instead.

Came up on freebsd, where libedit is apparently both builtin and
ancient, so configure rejected it; this caused PLIST divergence.