Hi X snapshots dated aug 3 and later are now built with XCB enabled. So libxcb and all the other xcb libs are provided, and libX11 now depends on it. Its major revision number has been incremented (it's now libX11.so.12.0) to avoid mixing things.
You will have to wait a bit until binary packages for your favourite architectures are updated to be able to really use them for new installs or upgrade. -- Matthieu Herrb
