We often need to deal with the value lattice that contains none and
undef as special values. A simple helper makes this much nicer.
I'd suggest that we look into this after D103860 landed. A lot of the aareturnedvalue handling is going away with that one. The gist here is that we can now look through the casts in scc_A, scc_B, and scc_C and therefore follow the returned call through the argument. This confuses the "unique return" logic.