DOS build is simply impossible, because SDL doesn't exist for it.
Have you looked into "Pocket UFO" ? it is an old version of the original game, which was adapted especially for Windows Mobile, with a vertical screen interface. It's completely unrelated to openxcom, so don't expect to have all the improvements and mods of openxcom, or support of Terror From the Deep. But it may be a much more comfortable way to play UFO game on your device.
https://www.xcomufo.com/x1dl.html
If you test it, can you please share your experience here? (what your machine is, how well PocketUFO runs, etc). Pocket PCs are uncommon, and even more rarely used as hand-held game consoles, I think a lot of people would be curious about this piece of XCOM history.
pocket pc have horizontal view, through dosbox I play in horizontal view
ofc i play Pocket UFO, and play alot, this version have alot of bugs,
invisible enemy, teleported beyond the borders of tactical map, enemy bases in water and crashing game when you try attack it, once enemy corpse start moving and fight never end, if you mindcontroled 1 hex of cyberdisck other 3 hex count last one licke enemy and they start to kill himself, if you do multiple missions without return to base you ammo starting not to spend, and most epic bug - aliens cant open door -defensing of the base is a peace a cake, all door at base automatic closes at end of turn
in my opinion it done on 70%
that because i play dos version through dosbox on my pocket pc