BUG? hstack/vstack/column_stack no longer accept generators

As reported by @ilayn over in https://github.com/numpy/numpy/issues/12262:

> There are other backwards incompatible changes for hstack and column_stack which were explicitly accepting generator expressions but now they don't.
>
> Xref : scipy/scipy#9405