COMPAT_FREEBD8 doesn't exists.

[Arseny Nasokin]

There was some talks back on 2011/2012 about this option, that kernel
should include it, but there is no such option (you can see at least
PR#163630 about this).

Also I've not found any commit which adds this option and no code in kernel
which depends on it.

Is note about this option should be nonexistent somewhere? Should it be
added to options as dummy?

-- Eir Nym