PR kern/20585 deals with setting COMPAT_NN options in the various
ports' GENERIC files (mostly).

The most important part of it was fixed long ago (adding COMPAT_16
everywhere).   While COMPAT_15 was never removed, all that does is
cost a trivial amount of kernel compilation time, no significant harm.

I haven't checked if the various MD uses of "#if 1 /* COMPAT_16 */"
all (or any) ever got changed to "#ifdef COMPAT_16" as they should
have, but I doubt that matters either.

I see no point in keeping this PR open, it is clear nothing more
is ever going to be done with it.

Please just close it.

kre