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/ewmh.h

@@ -17,7 +17,7 @@
  * and _NET_NUMBER_OF_DESKTOPS - 1.
  *
  */
-void ewmh_update_current_desktop();
+void ewmh_update_current_desktop(void);
 
 /**
  * Updates _NET_ACTIVE_WINDOW with the currently focused window.
@@ -44,6 +44,6 @@ void ewmh_update_client_list_stacking(xcb_window_t *stack, int num_windows);
  * Set up the EWMH hints on the root window.
  *
  */
-void ewmh_setup_hints();
+void ewmh_setup_hints(void);
 
 #endif