Who should honor WITHOUT_X11?

[Garrett Cooper]

Trying to build dbus recently on my system without X11 installed, I
ran into a few compile issues because I had put WITHOUT_X11=yes into
src.conf. However, I put WITHOUT_X11=yes into make.conf and was able
to compile dbus properly (in the end).

So, my questions are:
1. Should make.conf be responsible for the WITHOUT_X11 or should
another file be responsible for it?
2. Is it already documented in a manpage somewhere? It isn't
documented in `man make.conf'.

Thanks,
-Garrett