Auto merge of #1132 - glandium:master, r=alexcrichton
Auto merge of #1132 - glandium:master, r=alexcrichton

core::ffi::c_void is available since rustc 1.30

rust-lang-nursery/libc,rust-lang-nursery/libc,rust-lang/libc,rust-lang/libc,rust-lang/libc,rust-lang-nursery/libc