ENH: X11_SM_LIB should be advanced as well

Modules/FindX11.cmake

@@ -417,6 +417,7 @@ IF (UNIX)
     X11_XShm_INCLUDE_PATH
     X11_ICE_LIB
     X11_ICE_INCLUDE_PATH
+    X11_SM_LIB
   )
   SET(CMAKE_FIND_FRAMEWORK ${CMAKE_FIND_FRAMEWORK_SAVE})
 ENDIF (UNIX)