message: print sysroot build failure error
diff: @@ -137,9 +137,11 @@ pub fn setup(subcommand: &MiriCommand, target: &str, rustc_version: &VersionMeta
  .rustflags(rustflags)
  .cargo(cargo_cmd)
  .build_from_source(&rust_src)
  - .unwrap_or_else(|_| {
  - if only_setup {
  - show_error!("failed to build sysroot, see error details above")
  + .unwrap_or_else(|err| {
  + if print_sysroot {
  + show_error!("failed to build sysroot")
  + } else if only_setup {
  + show_error!("failed to build sysroot: {err:?}")
  } else {
  show_error!(
  "failed to build sysroot; run `cargo miri setup` to see the error details"
  