[sanxiyn]

Debian packages declare their supported architectures. "all" means it is architecture independent and will be available to a new architecture without rebuild. "any" means it is portable and will be available to a new architecture by rebuilding. In both cases no source change is needed.

Special packages (for example, compilers generating native code) enumerate supported architectures. For these packages, source change is needed, at least adding the name of the new architecture to the enumeration. But usually that's not the difficult part.