Check that the pkg-config file is available. This will be required
in the future to check whether xwayland supports features such as
-listenfd, -initfd or -verbose.
If there's no pkg-config file, check that the Xwayland executable
is available.
This effectively makes our relationship with xwayland closer to what
a dynamic library is: checked at build-time, but can be overridden
at run-time.
This is simply a false sense of security, and is worse than just using
setuid. CAP_SYS_ADMIN is an extremely serious capability that is
effectively as powerful as root.
It also required users to be in the input group, which allows any
process to keylog the entire system.
