The only reason polybar couldn't build without xkb is because the
xkeyboard module's source file was not removed during compilation.
xkeyboard already has an entry in unsupported.hpp
This effectively makes xcb-util-xkb optional
Following [1] to get to this setup.
We setup all the ccache configuration before calling project() because
project will perform compiler checks. This is also why we can't use
message_colored here and print the colors manually
Before ENABLE_CCACHE was not yet defined when we reached the check in
01-core because the option was defined in 02-opts
[1] https://crascit.com/2016/04/09/using-ccache-with-cmake/
