meson: Allow building on a Wayland-only environment
Currently, it is not possible to build spice-gtk on a Wayland-only environment due to the x11 dependency in meson. Since commit a7381b08 ("Allow to build without X11 gdk backend) it is possible to build spice-gtk without X11 GDK backend, so make the x11 dependency in meson optional. Signed-off-by:Fabio Estevam <festevam@denx.de> Acked-by:
Frediano Ziglio <freddy77@gmail.com>