We don't want to fallback to libwayland's defaults, so WAYLAND_DISPLAY
needs to be set in env. Since IPC in the future is going to use
XDG_RUNTIME_DIR, we also require it.
Because these functions will be used in other parts of the code as well,
we rework the build system slightly to accommodate it.
Co-authored-by: Érico Nogueira <erico.erc@gmail.com>
This rework is necessary because it will allow us to add signal handlers
via signalfd and a varlink interface for IPC.
Co-authored-by: Érico Nogueira <erico.erc@gmail.com>