building virtualbox-kmod with debugging

[Andriy Gapon]

This is a gentle reminder that DEBUG config option in virtualbox-ose-kmod ports
doesn't have proper (any?) effect.

On the other hand one can run make DEBUG_FLAGS="-O1 -g" to achieve a desired
effect in the same way as with "normal" kernel modules.  Of course the port
doesn't know to install the *.symbols files and they are not in pkg-plist.

BTW, WITH_CTF option also works from command line.

Would be nice to have these features conveniently integrated into the port.

-- 
Andriy Gapon