Concrete is fine, it can draw moisture from the ground which may cause the bedding to be damp; keep a deep litter base or clean often, good air exchange is also a good idea. Will also be fine for the horse, again, if it will stand in the stall for prolonged periods use a manure pack or line with 2" hard wood planking.

I would suggest using the rubber mats available at farm stores. They will add cushion for under the horse. However the stall will need to be bedded fairly deep to absorb urine from the horse. Bedding is needed to prevent mats from being slippery when wet. No place for wet to go on concreted base. Straw is a good padded bedding, in thick layers, just not as absorbent as sawdust or shavings. Some folks are using the woody pellets as bedding. You have to water them a little to start breaking up, but then they seem to do well by themselves.
Supposed to be quite dry, easy to clean once you have stall set up.
Mats under the chickens would keep cement moisture out of coop area bedding. Keep the birds slightly warmer, not as cold as cement. However chickens are messy and will still need a good bedding depth to keep dry, absorbative for poop.

Mats come in 4' x 6' pieces of heavy rubber. Thicker is better, stay in place better. We have 3/4". Most box stalls are 12' x 12'. Tie stalls are narrower, can depend on size of horse, 6' x 12' would fit almost any horse. Mats can be cut to fit, C-clamp or vise grips are best getting a grip on side edge for moving mats around. Cost a bit to get started, but mats make clean up very easy. Restful for the horse.