Clears gcc warnings:

xfontsel.c: In function ‘QuitAction’:
xfontsel.c:1477:1: warning: function might be candidate for
 attribute ‘noreturn’ [-Wsuggest-attribute=noreturn]
 QuitAction(Widget w, XEvent *event, String *params, Cardinal *num_params)
 ^~~~~~~~~~

xfontsel.c: In function ‘Quit’:
xfontsel.c:1392:6: warning: function might be candidate for
 attribute ‘noreturn’ [-Wsuggest-attribute=noreturn]
 void Quit(Widget w, XtPointer closure, XtPointer callData)
      ^~~~

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>