This patch enables support for nl80211. In case the libnl-genl-3.0
library isn't found, it will fall back to Wext instead.
The library to use can also be manually set with the CMake option
WITH_LIBNL.
The Wireless-Extensions (WE or Wext) are deprecated and long replaced
by cfg80211.
Although Wext isn't used by WiFi drivers anymore, CFG80211_WEXT allows
old tools to communicate with modern drivers by providing a wrapper
API.
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/
