-Zmiri-mute-stdout-stderr does not mute stderr

[matthiaskrgr]

fn main() {
	eprintln!("OH NO WHAT HAVE I DONE");
}

MIRIFLAGS="-Zmiri-mute-stdout-stderr" cargo miri run:

WARNING: Ignoring `RUSTC_WRAPPER` environment variable, Miri does not support wrapping.
    Finished dev [unoptimized + debuginfo] target(s) in 0.00s
     Running `/home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/cargo-miri target/miri/x86_64-unknown-linux-gnu/debug/f`
OH NO WHAT HAVE I DONE

cc @oli-obk