Intraconv shouldn't convert links to primitives

[jyn514]

Not sure how hard this is to implement - maybe not so bad since the HTML file has primitive in the name?

/home/joshua/src/rust/rust-clippy/clippy_lints/src/empty_enum.rs
================================================================

   16:  "    /// For further information visit [never type documentation](https://doc.rust-lang.org/std/primitive.never.html)"
        "    /// For further information visit [never type documentation](std::never)"

[jyn514]

I guess this could also be seen as a bug in rustdoc (rust-lang/rust#63351). But I don't think I'd expect std::never to work even if rust-lang/rust#63351 were fixed.