ports/61738: Downgrade port: devel/clanlib to 0.6.5.1

[Mark Linimon]

The submitter of ports/59964 has confirmed to me that this PR
supercedes that one.  Note: the repocopy to clanlib-devel, as
requested in 59964, has already been done, but not yet corrected
nor hooked up to the build.

Although I had taken that one, since I'm running way behind
this week, I think I'll let someone else take this one.