When GTK+ is built with Wayland support disabled (`-Dwayland_backend=false`), xfce4-panel fails to build with the following warning/error (depending on how the compiler treats implicit declarations; building with `--disable-wayland-client --disable-gtk-layer-shell`): ``` panel-application.c: In function ‘panel_application_init’: panel-application.c:249:13: warning: implicit declaration of function ‘gdk_wayland_display_query_registry’ [-Wimplicit-function-declaration] 249 | if (! gdk_wayland_display_query_registry (display, "zwlr_foreign_toplevel_manager_v1")) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ panel-application.c:249:13: warning: nested extern declaration of ‘gdk_wayland_display_query_registry’ [-Wnested-externs] ``` Original bug report: https://bugs.gentoo.org/903802