[Hexagon] Use BUILD_PAIR to expand i128 instead of doing arithmetic

    if (BitWidth == 64)

      return Combines[0];

    // It must be i128. I128 is not a legal type, so this part will be

    // executed during type legalization. We need to generate code that

    // the default expansion can break up into smaller pieces.

    SDValue C0 = DAG.getZExtOrTrunc(Combines[0], dl, ResTy);

    SDValue C1 = DAG.getNode(ISD::SHL, dl, ResTy,

        DAG.getZExtOrTrunc(Combines[1], dl, ResTy),

        DAG.getConstant(64, dl, MVT::i32));

    return DAG.getNode(ISD::OR, dl, ResTy, C0, C1);

    return DAG.getNode(ISD::BUILD_PAIR, dl, ResTy, Combines);

  }

  return Op;