Predicate failure during translation of call to native returning generic type

[brson]

native mod m {
    fn cast<T>() -> T;
}

type t<T> = { t: T };

fn main() {
    let i: t<int> = m::cast();
}

rust: upcall fail 'Predicate type_has_static_size(ccx, ret_ty) failed', ../src/comp/middle/trans.rs:3851
rust: domain main @0x9745e38 root task failed

[nikomatsakis]

Yes, there are some dubious checks in various places. I looked into fixing this. I believe the best way is to (a) use wrappers around native functions and (b) translate native functions with dynamically sized return values so that they use an initial pointer as the return type. This would fit well with the C convention of inserting silent structure arguments. We should probably do the same for structure return types to cdecl functions; LLVM would probably do it for us, but that will yield a second copy. Not sure how STDCALL functions handle this case.

[catamorphism]

Obsolete. Checks were removed at some point IIRC, plus type_has_static_size doesn't seem to exist at all.