Codegen issue: box mut dyn trait unhandled codegen_pointer_cast

[adpaco-aws]

use std::io::{sink, Write};

fn main() {
    let mut log : Box<dyn Write + Send> = Box::new(sink());
    let dest : Box<dyn Write + Send> = Box::new(log.as_mut());
}

Fails with an unhandled pointer cast exception.

[danielsn]

May be resolved by #33