This is a huge hack... We temporarily create a new node with the
correct structure and use that for printing.
I think it would be better to always use a separate node type for
NewAnonClass, rather than using a combination of New and Class,
but this would require some larger changes, as this node type would
have to be both Expr and ClassLike, which is not possible right now,
as the latter is a class rather than an interface...
