To calculate the V approach the FMS is using a wind either taken by the ADIRS or inserted on APPR PERF page. At first I will say that it takes the wind inserted by the crew, but I am not completed sure about this assumption since the MINI FUNCTION on A320 will need as well wind info taken by ADIRS to be able to cope with sudden loss of headwind / increase tailwind.
It uses the wind entered in the PERF APPR page to correct the computed VAPP:
Takeoff, performance and go around speeds
The FMGC uses the performance model and either the predicted landing weight or the current gross weight at transition to the approach phase to compute approach speeds (VLS, VAPP, F, S, Green Dot). On the PERF APPR page, the selected LDG CONF determines the applicable VLS and VAPP, the latter being updated by the WIND correction that the pilot enters on the same page.
(A320 FCOM - Autoflight - Flight Management - Performance, emphasis mine)