Depend on libc from crates.io

src/librustc_interface/Cargo.toml

@@ -10,6 +10,7 @@ path = "lib.rs"
 doctest = false
 
 [dependencies]
+libc = "0.2"
 log = "0.4"
 rayon = { version = "0.3.0", package = "rustc-rayon" }
 smallvec = { version = "1.0", features = ["union", "may_dangle"] }

src/librustc_interface/lib.rs

@@ -6,9 +6,6 @@
 #![feature(generators)]
 #![recursion_limit = "256"]
 
-#[cfg(unix)]
-extern crate libc;
-
 mod callbacks;
 pub mod interface;
 mod passes;