With the crates.io distribution of libc (#20606) in my Cargo.toml: ``` [dependencies] libc = "0.1" ``` I still get a warning on `extern crate libc`: ``` lib.rs:6:1: 6:19 warning: use of unstable library feature 'libc' lib.rs:6 extern crate libc; ^~~~~~~~~~~~~~~~~~ lib.rs:6:1: 6:19 help: add #![feature(libc)] to the crate attributes to silence this warning lib.rs:6 extern crate libc; ^~~~~~~~~~~~~~~~~~ ``` Am I linking to the wrong crate? How do you choose the version from cargo over the version included in rustc?