message: avoid injected_panic_runtime which is going away
diff: @@ -135,7 +135,11 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  // Normally, this will be either `libpanic_unwind` or `libpanic_abort`, but it could
  // also be a custom user-provided implementation via `#![feature(panic_runtime)]`
  "__rust_start_panic" => {
  - let panic_runtime = tcx.crate_name(tcx.injected_panic_runtime().expect("No panic runtime found!"));
  + // FIXME we might want to cache this... but it's not really performance-critical.
  + let panic_runtime = tcx.crates().iter()
  + .find(|cnum| tcx.is_panic_runtime(**cnum))
  + .expect("No panic runtime found!");
  + let panic_runtime = tcx.crate_name(*panic_runtime);
  let start_panic_instance = this.resolve_path(&[&*panic_runtime.as_str(), "__rust_start_panic"])?;
  return Ok(Some(this.load_mir(start_panic_instance.def, None)?));
  }
  