This fixes several latent bugs where code went down the path with double buffering enabled when it wasn't, and vice versa. * src/xfns.c (x_set_inhibit_double_buffering): Improve commentary and only define when HAVE_XDBE. (x_mark_frame_dirty): Only set buffer flip flag when HAVE_XDBE. (initial_set_up_x_back_buffer): Clean up coding style and remove unnecessary block_input pair. (Fx_double_buffered_p): Always return nil if !HAVE_XDBE. (x_frame_parm_handlers): Don't set double buffering handler if !HAVE_XDBE. * src/xftfont.c (xftfont_drop_xrender_surfaces, xftfont_driver): Only define when XDBE is available. * src/xterm.c (x_drop_xrender_surfaces): Likewise. (x_clear_window): Don't test double buffering flags when !HAVE_XDBE. (show_back_buffer): Only define when HAVE_XDBE. (x_flip_and_flush): Don't try to flip when !HAVE_XDBE. (XTframe_up_to_date): Likewise. (XTbuffer_flipping_unblocked_hook): Only define when Xdbe is available. (x_clear_area): Don't test double buffering flags when Xdbe is not available. (flush_dirty_back_buffer_on): Don't define if there's no DBE. (handle_one_xevent, x_create_terminal): Likewise. * src/xterm.h (FRAME_X_DRAWABLE): Fix coding style.