I do, but that's just a plumbing feature not a room in itself.
The term washroom works for me. I've never seen a room with a toilet that didn't also have a sink for washing your hands afterward. I hope I never do.
The first place I rented in London was like that. They'd built a wall up the middle of the original bathroom, separating it into a small room with a toilet and a larger room with a bath and basin. Not the nicest or most practical arrangement.