Ingsoc85: As GOG will also act as a publisher on this one, they could modify the game code to suit it to modern machine.
JMich: To modify a game's code before selling it, 3 things are required.
1) The publisher's permission.
2) The game's code.
3) People who can actually modify said code.
While GOG will have 1, it's not sure they will have 2 and/or 3. I doubt the game's code will be modified any time soon.
As an alternative to 2 and 3, people who are able to reverse engineer the compiled code and change it using tools such as a hex editor. This is much harder than just changing the source code and recompiling, but it is possible (I've done this a couple times).
Also, you are missing one other thing: For 2 and 3, you also need to have a compiler that can compile the code, as well as everything else the compilation needs. A modern compiler will not necessarily work, as languages and libraries change over time, and different versions of the same compiler will have different bugs (and code might rely on compiler bugs to function as intended).
I can confirm this.