Associated functions on reexported private types cause linker errors

This is the same issue as #9790, but with associated functions (aka "static methods".)

Test case:

lib.rs:

```
pub use internal::S;
mod internal {
    pub struct S;
    impl S {
        pub fn test() {}
    }
}
```

main.rs:

```
extern mod lib;
fn main() {
    lib::S::test()
}
```

CC: @alexcrichton 
