"unconstrained type" in ccross with templates

[mrwright]

The following code:

enum X<T> {
    Some(*T)
}

fn f<T>() -> *T {
    match *(null as *X<T>) {
        Some(x) => null as *T,
    }
}

fails with:

task '<main>' failed at 'Type is not fully constrained: <unconstrained>', src/target/ccross.rs:436

If the cast of null to *T is removed, it works.

[mrwright]

Another way to trigger what I assume is the same bug:

fn f<T>() -> *T {
    null
}

fn g<T>() -> *T {
    f()
}