Native "llvm" modules don't work

[brson]

There is some support for modules of the form

native "llvm" mod llvm {
    fn sqrt(n: float) -> float = "sqrt.f64";
}

which are intended to generate calls to llvm intrinsics. In the one case we're actually using this (the above example from shootout-nbody) we are actually just generating a call to function sqrt which happens to be in the c standard library.

I've also added a failing test in run-pass/native-llvm.rs.

Personally I think we should drop this functionality.

[brson]

This ABI has been removed