meta-pkgs/modular-xorg/avoid-duplicate.mk doesn't work

[David Holland <dholland-pkgtech%netbsd.org@localhost>]

At some point recently meta-pkgs/modular-xorg/avoid-duplicate.mk was
added to avoid trying to build pkgsrc xorg packages for native X.
Unfortunately, it doesn't work.

It includes the package's own builtin.mk and tests USE_BUILTIN.pkg as
part of the decision. Unfortunately, the builtin.mk logic in most/all
packages is meant for use when buildlinking, and not for the package
itself. Consequently, this use bypasses the logic in bsd.bl3.mk that
makes sure that if package P is not builtin, then package Q that
depends on P can't be either.

Thus in situations where a builtin package cannot be used because
something it depends on is built from pkgsrc, it produces the wrong
answer and rejects the build.

This happens with libXft on -8 because the native freetype2 and/or
fontconfig that it depends on are too old or unsuitable or something
(forget what), and then nothing that depends on libXft (which is a
lot because it includes gtk) will build. Someone reported this in chat
the other day and I stepped it it myself today.

There is no easy solution for this problem so I think we'd better
disable the feature for Q1. After that... we can probably refactor
that logic to make it available for this purpose, but that's a fairly
big deal I'm afraid.

-- 
David A. Holland
dholland%netbsd.org@localhost