glutin refuses to compile on OS X

```
~/.cargo/git/checkouts/glutin-666c1766c69e6584/master/src/cocoa/mod.rs:145:36: 145:82 error: mismatched types:
 expected `*mut libc::types::common::c95::c_void`,
    found `*mut libc::types::common::c95::c_void`
 (expected enum `libc::types::common::c95::c_void`,
    found a different enum `libc::types::common::c95::c_void`) [E0308]
```

Is this a compiler bug or something?
