When remapping generator expressions / set+dict comprehensions,
we create an explicit new function, which will later get run
through CFG again.  With the new changes, we can't use a nodeName()
that was generated in the parent scope, since that will end up clashing
when the generated scope generates its own names.

I think it's not too bad to fix since in these cases the arguments are only
ever used inside of the inner scope, so we just have to use names that aren't
used elsewhere.