message: skip installing rust-src if XARGO_RUST_SRC is set
diff: @@ -193,7 +193,9 @@ fn setup(ask_user: bool) {
  }
  }
  - // Then, we also need rust-src. Let's see if it is already installed.
  + // Then, unless XARGO_RUST_SRC is set, we also need rust-src.
  + // Let's see if it is already installed.
  + if std::env::var("XARGO_RUST_SRC").is_err() {
  let sysroot = Command::new("rustc").args(&["--print", "sysroot"]).output().unwrap().stdout;
  let sysroot = std::str::from_utf8(&sysroot[..]).unwrap();
  let src = Path::new(sysroot.trim_end_matches('\n')).join("lib").join("rustlib").join("src");
  @@ -207,6 +209,7 @@ fn setup(ask_user: bool) {
  show_error(format!("Failed to install rust-src component"));
  }
  }
  + }
  // Next, we need our own libstd. We will do this work in whatever is a good cache dir for this platform.
  let dirs = directories::ProjectDirs::from("miri", "miri", "miri").unwrap();
  