message: honor CARGO env var (for rustc bootstrap)
diff: @@ -231,7 +231,14 @@ fn setup(ask_user: bool) {
  } else {
  println!("Installing xargo: `cargo install xargo -f`");
  }
  - if !Command::new("cargo").args(&["install", "xargo", "-f"]).status().unwrap().success() {
  +
  + let mut cargo = if let Ok(val) = std::env::var("CARGO") {
  + // In rustc bootstrap, an env var tells us where to find cargo.
  + Command::new(val)
  + } else {
  + Command::new("cargo")
  + };
  + if !cargo.args(&["install", "xargo", "-f"]).status().unwrap().success() {
  show_error(format!("Failed to install xargo"));
  }
  }
  