xwayland: Check for listenfd option
Current Xwayland has marked the command line option "-listen" as deprecated in favor of "-listenfd".
Use the pkg-config variable "have_listenfd" (if available) from Xwayland to determine if we should use that option, to avoid a deprecation warning when spawning Xwayland.
See-also: https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/593