Use (void) instead of () for functions without args (Thanks fernandotcl)

See also:
http://article.gmane.org/gmane.linux.kernel/1268792

The C compiler will handle (void) as "no arguments" and () as "variadic
function" (equivalent to (...)) which might lead to subtle errors, such
as the one which was fixed with commit 0ea64ae4.

include/xcursor.h

@@ -20,7 +20,7 @@ enum xcursor_cursor_t {
     XCURSOR_CURSOR_MAX
 };
 
-void xcursor_load_cursors();
+void xcursor_load_cursors(void);
 Cursor xcursor_get_cursor(enum xcursor_cursor_t c);
 int xcursor_get_xcb_cursor(enum xcursor_cursor_t c);