For `cargo install` we'll now show a more specific parse error for
semver, much like other parts of cargo.
This came out of my work on #12801. I was looking at what might be
appropriate to put in a `cargo-util-semver` crate and realized we have
the `ToSemver` trait that exists but doesn't do much, so I dropped it.
This is a short-term option until we can have a better solution for
globbing. This does not update `benches/` to support which has a README
in there preventing globbing; this seems low-churn enough not to find a
solution for it.
On the next sync-up with rust-lang/rust, we'll need to update 4e46301258/src/bootstrap/tool.rs (L588-L603)Fixes#11988