If you plan to use extruded polystyrene, go ahead and put the vapor barrier against the masonry. Remember to tape the seams with foil tape, or it won't be an affective vapor barrier.
The reason a vapor barrier is supposed to go on the warm side is that, like heat, moisture vapor always moves from the warm side toward the cold side. So in an insulated house wall (assuming heating season, not southern Florida in July) the moisture goes from the room side toward the outside. If the outside is cold enough, there is a dew point somewhere between the inside and the outside. With fiberglass batt insulation, what you really REALLY don't want is to have the moisture condensing somewhere in the middle of your insulation batts. First, soggy fiberglass doesn't insulate well. Second, wet, soggy batts lead to rotted framing lumber, and to mold.
But Styrofoam (the extruded polystyrene) is "closed cell" polystyrene. It won't absorb moisture so you shouldn't have to worry about rot or mold. But you should still keep your framing studs an inch (or at least a half inch) clear of the masonry so that if any moisture condenses on the inside surface, it won't soak the studs.
