message: add special exception for std_miri_test crate to call std-only functions
diff: @@ -803,7 +803,12 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  // Fall back to the instance of the function itself.
  let instance = instance.unwrap_or(frame.instance);
  // Now check if this is in the same crate as start_fn.
  - this.tcx.def_path(instance.def_id()).krate == this.tcx.def_path(start_fn).krate
  + // As a special exception we also allow unit tests from
  + // <https://github.com/rust-lang/miri-test-libstd/tree/master/std_miri_test> to call these
  + // shims.
  + let frame_crate = this.tcx.def_path(instance.def_id()).krate;
  + frame_crate == this.tcx.def_path(start_fn).krate
  + || this.tcx.crate_name(frame_crate).as_str() == "std_miri_test"
  }
  /// Handler that should be called when unsupported functionality is encountered.
  