mainwindow: gated gdk_wayland_* calls behind version check

This should ensure, that NoteKit will continue to be build on RHEL 8.

mainwindow.cpp

@@ -793,6 +793,7 @@ void CMainWindow::SettingCsdUpdate() {
 	 * unable to change the decorations after it's initial set, so
 	 * NoteKit had to be restarted in order to have proper decorations.
 	 */
+	#if GTK_CHECK_VERSION (3,22,0)
 	#ifdef GDK_WINDOWING_WAYLAND
 		if (GDK_IS_WAYLAND_DISPLAY (gdk_window_get_display(window))) {
 			if (state) {
@@ -802,6 +803,7 @@ void CMainWindow::SettingCsdUpdate() {
 			}
 		}
 	#endif
+	#endif
 	/*
 	 * TODO: here is space for potential support of broadway, w32 & quartz:
 	 * IMO broadway support for SSD irrelevant, as it doesn't make much sense.