Better way to do conditional inclusion in make

[NGie Cooper]

On Thu, Feb 5, 2015 at 4:41 PM, Julian Elischer <julian at freebsd.org> wrote:

...

> how does it cope with the case where a single file is dependent on either of
> two options.
> (we have this in our tree.. not sure if it occurs in the FreeBSD tree.)
> file could occur in both lists or twice in one list..

This is a good, valid point. I think that Warner's proposal will fix
the simple case (using one knob), but not the more complex case.

What concerns me about the short description of the implementation,
(and something that I'm going to add to the phabricator review) is
that this will:

1. Break using FILESGROUPS
2. Requires creating snippets for dealing with magic in bsd.*.mk (I
wouldn't want this magic going into the general purpose snippets
because it would probably break backwards compatibility).

Thanks!