[feature(set_stdio)] has been removed

rust-lang/rust@aff7bd66e8b moves the two apis into one, and then a later commit makes them take a Vec directly since that is the destination for Rust's one internal consumer (test).  Seems like either we need to RFC a supported api into Rust to make wasm-glue possible, or the wasm target compiler should already redirect stdout and stderr to the javascript console.log and/or both.