Derivative works aren't some unknowable arcane legal term. They're a pretty fundamental aspect of copyright law. The canonical examples of derivative works are things like adaptation of a book to a film, translation of a book, or a sequel.

And given these examples, it's very clear that recompilation to play on modern hardware is quite similar in spirit to translating a book into a different language, which makes it a derivative work. The other alternative is that there is insufficient creativity in the recompilation effort to merit independent copyright at all, in which case it's just plain copying of the original work. In either case, it's infringement.