Package wip/xorg-server dependency issue

[Thomas Schlesinger <schlesinger%netcologne.de@localhost>]

Hi,

I've installed Xorg 6.9.0 (x11/xorg-server) and would like to update to 
modular Xorg (wip/xorg-server). A depedency of this package is wip/libICE. 
But libICE doesn't build, because it can't find xproto:

[..]
 checking pkg-config is at least version 0.9.0... yes
checking for ICE... gnome-config: not found
configure: error: Package requirements (xproto) were not met:

No package 'xproto' found
[..]

x11/xproto-7.0.4 is installed on my system.

Any suggestions?

Thomas