Thanks @dcaliste for the answer.
I was trying to make Amazfish run on 4.1.0 (I am not the author, of course) and noticed this unavailable symbol when (after adding some libicu links) :
So my first thought was, cool, let’s use another ExtendedCalendar constructor, that’s common between the two mkcal versions. Unfortunately there isn’t a such common API.
So I was thinking - how would one fix this, if you’d like to release both for SFOS 4.0 and 4.1? Maybe packages could be upgraded on the older release too. Unfortunately they aren’t, either - admittedly it would cause breakages on 4.0 if it would update…
So I think the problem is that the mkcal API is not in any way compatible between these two sampled versions, nor forward or backward.
This was before 4.1 target was released. Compiling on 4.1 should fix it for me, but I what is the solution in general for these kind of situations?