This seems to be an artifact of using Qt Creator. Generally speaking it is just a matter of running the same compilation steps with different targets (so long as you don't have arch-specific stuff in there like reliance on aliasing behavior or specialized simd, of course). Qt uses just about the most complicated build process I've seen outside of Xcode/objective-c++.
I'm curious to compare what the GTK build process looks like as a universal binary; I think RawTherapee has done it.
I'm curious to compare what the GTK build process looks like as a universal binary; I think RawTherapee has done it.