The outer layer should be wind proof/wind resistant. Make sure you get something that can breathe as opposed to being completely wind or rain proof. The outer layer can be just a shell. Fleece is good as a middle layer. A wool or other wicking material can be used for the base layer. The base layer should be relatively thin and fit close to the skin but not so tight that it restricts circulation.
It doesn't matter so much what activities the layers were intended for. Often cycling specific stuff is expensive and not typically designed for really cold weather, but, like anything else it can be used in combination with other garments in layers to achieve the necessary warmth.
The only thing I need that's cycling specific is something with a chamois (pad). Some folks get by fine without one, and I won't bother with one if I'm only riding a few miles.
So in the winter I don't wear anything cycling specific on my upper body. For my lower body I'll wear padded cycling shorts or tights under another layer. I do have a set of Pearl Izumi Amfib bib tights but don't use them that often. I prefer a pair Craft X-Country ski windproof tights over cycling tights or shorts. They have an articulated knee that flexes easier than the Amfibs and they're not as noisy. ;-)