Don't use emit_parts_list for regular operations.
    
    Using emit_parts_list does not make sense for any
    operation except Ialloc, where we can delay the
    computation of simple expression until the allocation
    is done. So we try to avoid using emit_parts_list for
    regular operations, where the special treatment of
    non simple expression conflicts with our special
    instruction selection on arm (and arm64). For example
    we cannot merge the add and shift operation required
    for tagging as soon as there is at least one non
    simple expression involved, even though both Cadd
    and Clsl do not care at all whether its arguments are
    simple or not.
    
    git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14292 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02