xwayland: Check for listenfd option

Olivier Fourdan requested to merge ofourdan/mutter:have-listenfd-check into master

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

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