games/super_methane_brothers: unbreak after r450353

In file included from sources/game.cpp:28:
In file included from sources/target.h:21:
In file included from /usr/local/include/ClanLib-2.3/ClanLib/display.h:112:
In file included from /usr/local/include/ClanLib-2.3/ClanLib/Display/TargetProviders/display_window_provider.h:44:
/usr/local/include/ClanLib-2.3/ClanLib/Display/TargetProviders/../Window/display_window.h:48:10: fatal error: 'X11/Xlib.h' file not found
#include <X11/Xlib.h>

^