That's not how Apple development works. You code to their API using their dev tools and their compiler, and they will take care of it for you.
It sounds wild, but look at their history.
Apps built on Cocoa only needed a recompile to run on the new CPU arch when they switched to x86. Carbon-based apps could be a little more involved because it was their older API.
Yes, they had Rosetta, but that was only to translate unsupported legacy applications.
Actually, their whole migration to x86 impressed me more than the iPhone ever has.