Everything trying to link to readline is already passing -lreadline when needed
so all that is needed here is to pass the right path where to find it.
Reported by: peter
For minimal breakage reasons, DragonFly has OSVERSION set to the
equivalent of FreeBSD 99. When the readline compatibility for FreeBSD
10 was revoked recently, it broke a lot of dports.
Restore the default to how it was before on DragonFly only to restore
those ports using OPSYS.
Approved by: portmgr (bapt)
