`crabtime` does not work with `-Zfmt-debug=none`

[purpole]

I tried to use a project with crabtime that uses the -Zfmt-debug=none flag via .cargo/config.toml, however the macro did not produce any output.

To quickly fix this in my project, I patched the run_cargo_project function to just use empty RUSTFLAGS:

let output = Command::new("cargo")
    .env("RUSTFLAGS", "")
    .arg("run")
    .arg("--target")
    .arg(&host_target)
    .current_dir(project_dir)
    .output()
    .context("Failed to execute cargo run")?;

Currently, it seems like all options from .cargo/config.toml of the project using crabtime are used to compile crabtime, is this necessary? 🙂