fns using c-stack-cdecl native ABI cannot be used as values

[nikomatsakis]

this test (src/test/run-pass/c-stack-as-value.rs) yields a LLVM compilation error:

// xfail-test

native "c-stack-cdecl" mod rustrt {
    fn unsupervise();
}

fn main() {
    let _foo = rustrt::unsupervise;
}

[nikomatsakis]

Fixed in @b6af844