Greetings Guix,

I am the maintainer of this package in NixOS and figured I could update
it here as well, since it was non-trivial.

The libx11 dependency is dropped in favour of a new xcb-util-xrm module.
I added the latter to xdisorg since it's not listed on xcb.fd.o proper,
but followed the convention of the other xcb-util-* libraries.

Disclaimer: untested, apart from building with rounds=2.