I assume that you are not actually trying to be USB3 compliant.
Do you mean you just want to use the cable, or do you want to use USB3 cable drivers?
If the former (i.e. you are just using the cable), the impedance is supposed to be 90ohm (differential), which is close enough to the Xilinx transceiver impedance. You will need AC coupling capacitors on at least one end of the link.