message: make attempt to cross-interpret a hard error
diff: @@ -923,8 +923,7 @@ fn phase_cargo_rustdoc(fst_arg: &str, mut args: env::Args) {
  }
  if crossmode {
  - eprintln!("Cross-interpreting doc-tests is not currently supported by Miri.");
  - return;
  + show_error(format!("cross-interpreting doc-tests is not currently supported by Miri."));
  }
  // For each doc-test, rustdoc starts two child processes: first the test is compiled,
  