rust-lang/rust — pull request #20237 by Ericson2314 (2014-12-26 04:20:17+00:00)
Title: liballoc does not need liblibc under certain configurations

libc is only used when the heap allocations are not defined externally, or defined in another crate. I assume these extern* configurations were added for the sake of those of us experimenting with freestanding Rust. Avoiding libc where possible is often very important for us.