Add additional toolchains maintained by cross-rs.

[Alexhuszagh]

These toolchains are not automatically tested by CI, and must be built manually by the user. However, they are confirmed to build at least once, and are likely to work as-is.

[Alexhuszagh]

I think that's everything. We now locate the Dockerfiles ahead of time, allowing mixing and matching in the docker root or the cross-toolchain docker root:

fn locate_dockerfile(
    target: String,
    docker_root: &Path,
    cross_toolchain_root: &Path,
) -> cross::Result<(String, String)> {
    let dockerfile_name = format!("Dockerfile.{target}");
    let dockerfile_root = if cross_toolchain_root.join(&dockerfile_name).exists() {
        &cross_toolchain_root
    } else if docker_root.join(&dockerfile_name).exists() {
        &docker_root
    } else {
        eyre::bail!("unable to find dockerfile for target \"{target}\"");
    };
    let dockerfile = dockerfile_root.join(dockerfile_name).display().to_string();
    Ok((target, dockerfile))
}

...

pub fn build_docker_image(...) -> cross::Result<()> {
    ....
    let targets = targets
        .into_iter()
        .map(|t| locate_dockerfile(t, &docker_root, &cross_toolchains_root))
        .collect::<cross::Result<Vec<_>>>()?;

    let mut results = vec![];
    for (target, dockerfile) in &targets {
        ....
    }

    ....
}

[Emilgardis]

bors r+

[bors]

Build succeeded:

• conclusion