message: Don't `unwrap()` in `in_std()`
diff: @@ -631,8 +631,10 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  fn in_std(&self) -> bool {
  let this = self.eval_context_ref();
  + this.tcx.lang_items().start_fn().map_or(false, |start_fn| {
  this.tcx.def_path(this.frame().instance.def_id()).krate
  - == this.tcx.def_path(this.tcx.lang_items().start_fn().unwrap()).krate
  + == this.tcx.def_path(start_fn).krate
  + })
  }
  }
  