Hi RG,

since cairo is meant to be a portable and backend-agnostic vector graphics
library, I find it hard to believe it needs to propagate fontconfig, freetype,
glib, libpng, pixman, x11, xcb, xext and xrender.

Are you sure that cairo actually exposes those libraries' interfaces to its
users?

The cairo.pc file also suggests otherwise:

Requires.private:   gobject-2.0 glib-2.0 >= 2.14       pixman-1 >= 0.30.0    fontconfig >= 2.2.95 freetype2 >= 9.7.3   libpng xcb-shm xcb >= 1.6 xcb-render >= 1.6 xrender >= 0.6 x11 xext 
Libs: -L${libdir} -lcairo
Libs.private:            -lz -lz   -lz      

"Requires.private" means that those are implementation details and not to be
exposed to the users of the library.

Also, please do not make libsigc++ public twice.  It's already in the
module's #:export list.

Same for glibmm and maybe others.

Pushed the pixman and hplip patches to wip-desktop.