Fix GTK 3.x compiler warnings

[tanuki-no]

This patch replces outdated API functions with newer ones:

display.c: In function ‘update_window’:
display.c:153:9: warning: ‘gdk_cairo_create’ is deprecated: Use 'gdk_window_begin_draw_frame() and gdk_drawing_context_get_cairo_context()' instead [-Wdeprecated-declarations]
153 | cairo_t *cr = gdk_cairo_create(drawable);
| ^~~~~~~
In file included from /usr/include/gtk-3.0/gdk/gdk.h:33,
from /usr/include/gtk-3.0/gtk/gtk.h:30,
from display.c:23:
/usr/include/gtk-3.0/gdk/gdkcairo.h:35:12: note: declared here
35 | cairo_t * gdk_cairo_create (GdkWindow *window);
| ^~~~~~~~~~~~~~~~
display.c: In function ‘button_release_event’:
display.c:323:9: warning: ‘gdk_cairo_create’ is deprecated: Use 'gdk_window_begin_draw_frame() and gdk_drawing_context_get_cairo_context()' instead [-Wdeprecated-declarations]
323 | cairo_t *cr = gdk_cairo_create(drawable);
| ^~~~~~~
/usr/include/gtk-3.0/gdk/gdkcairo.h:35:12: note: declared here
35 | cairo_t * gdk_cairo_create (GdkWindow window);
| ^~~~~~~~~~~~~~~~
display.c:330:9: warning: ‘gdk_flush’ is deprecated: Use 'gdk_display_flush' instead [-Wdeprecated-declarations]
330 | gdk_flush(); / force X to actually draw the damn thing. */
| ^~~~~~~~~
In file included from /usr/include/gtk-3.0/gdk/gdk.h:50:
/usr/include/gtk-3.0/gdk/gdkmain.h:124:6: note: declared here
124 | void gdk_flush (void);
| ^~~~~~~~~
display.c: In function ‘display_send_img’:
display.c:64:5: warning: ignoring return value of ‘write’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
64 | write(imgpipe_writefd, name, len);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
display.c: In function ‘do_image_display’:
display.c:73:5: warning: ignoring return value of ‘pipe’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
73 | pipe(pfd);
| ^~~~~~~~~
display.c: In function ‘pipe_event’:
display.c:420:29: warning: ignoring return value of ‘write’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
420 | write(1, "\a", 1);
| ^~~~~~~~~~~~~~~~~
rm -f libdisplay.a

Signed-off-by: Vladislav Mikhailikov vmikhailikov@gmail.com

[tanuki-no]

Adding PR to fix the reported issue: #58