fn eval_body_using_ecx<'mir, 'tcx>(
    ecx: &mut InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>,
    cid: GlobalId<'tcx>,
    body: &'mir Body<'tcx>
) -> InterpResult<'tcx, MPlaceTy<'tcx>>