`static TEST: (~str, ~str) = (~"foo", ~"bar")` is not allowed and it would fail with `static items are not allowed to have owned pointers`, instead `&'static [~"foo", ~"bar"]` would fail to compile because vectors are not allowed in constant expressions.

I tried to keep the amount of code changes in the visitor low because both of these functions could be used elsewhere. Therefore, matching on `ItemStatic` and checking the expression made sense to me.