Private enum variant reexport error emits an error per each variant

[estebank]

When trying to reexport the variants of a private enum, a diagnostic is emitted for each variant pointing always at the same reexport span, making it too verbose:

error: variant `Variant1` is private, and cannot be reexported, consider declaring its enum as `pub`
  --> file.rs:12:9
   |
12 | pub use self::Enum::*;
   |         ^^^^^^^^^^^^^
(...)
error: variant `VariantN` is private, and cannot be reexported, consider declaring its enum as `pub`
  --> file.rs:12:9
   |
12 | pub use self::Enum::*;
   |         ^^^^^^^^^^^^^

Ideally there would be only one diagnostic emitted, with an extra span pointing at the definition of Enum to suggest making it public.

[zackmdavis]

I have a vision for this.