message: fix layout in discriminant_value
diff: @@ -250,8 +250,7 @@ impl<'a, 'mir, 'tcx> EvalContextExt<'tcx> for EvalContext<'a, 'mir, 'tcx, super:
  let adt_align = self.layout_of(args[0].ty)?.align;
  let place = Place::from_scalar_ptr(adt_ptr, adt_align);
  let discr_val = self.read_discriminant_value(place, layout)?;
  - let ptr_size = self.memory.pointer_size();
  - self.write_scalar(dest, Scalar::from_uint(discr_val, ptr_size), dest_layout.ty)?;
  + self.write_scalar(dest, Scalar::from_uint(discr_val, dest_layout.size), dest_layout.ty)?;
  }
  "sinf32" | "fabsf32" | "cosf32" | "sqrtf32" | "expf32" | "exp2f32" | "logf32" |
  