rustc-ap-rustc_cratesio_shim 491.0.0

Automatically published version of the package `rustc_cratesio_shim` in the rust-lang/rust repository from commit 6312b89fdabce0aedf613391266e08c0deef2324 The publishing script for this crate lives at: https://github.com/alexcrichton/rustc-auto-publish