The use of AvoidUnalignedAccesses option for these cases doen't much sense to me.
Assembler routines like `revb_h_h_u` and `revb_h_h` will emit 5 instructions when Zbb
extension is not available. This is more than the case when AvoidUnalignedAccesses option
is true. After this change, we always emit 4 instructions compared to 3 instrucions in
the case when we have Zbb extension. But I don't think it will make a difference.