modular-xorg-server needs printproto(?)

[walt <wa1ter%myrealbox.com@localhost>]

When building modular-xorg-server, the configure script fails to
detect printproto even when it is installed.  There is some code
in the xorg-server package which can use printproto, even though
the package builds without error when printproto is 'missing'.

modular-xorg-libs pulls in printproto automatically, so it seems
reasonable to allow xorg-server to use printproto, yes?

Anyway, I find that adding  printproto/buildlink3.mk to the
Makefile for modular-xorg-server fixes the problem.  If there
really is a problem here, that is.  I don't know what difference
it makes, one way or the other.