I dunno, a bootloader seems like the most clear-cut example of something not being a derived work you could get - it doesn't care about the code being bootloeaded and vice-versa, and the API between the two is about as trivial as it can get. What matters according to the GPL isn't whether the code runs on other platforms but how deeply intertwined it is with the kernel; for most Linux drivers, whether it runs on other platforms is a good rule of thumb for determining this, but it kind of breaks down for ESX.

Also, "retrospectively making something portable doesn't change it's previous status as a derived work" was if I'm not mistaken SCO's argument for why it should be illegal for customers to run software they'd developed on SCO Unix under Linux. It's not something we should be supporting because it'd a really dangerous tool for locking users into a particular OS. (Fortunately, SCO lost.)