the git version of libxcb fails to build without the git-version of xcb-proto. Please update dependency.
Once you have -9999 of xcb-proto on your system, and then you update libxcb a year later after some ABI break(s), you're still going to have to update xcb-proto again.
I don't think we have any sort of way to handle this. Whether the dependency is on >=xcb-proto-1.6 or >=xcb-proto-9999 I think is immaterial.