No, the stall speed concerns the speed of the aircraft relative to the surrounding air (the IAS). How fast the aircraft is moving relative to the ground is irrelevant. In your example, with a headwind of 20 kts and IAS 100 kts, you are moving 80 kts relative to the ground, but the stall speed is always given for IAS.
Re: the L-39, I'm pretty sure there's no readout for ground speed, although there is a separate readout for true airspeed.