You can build with -Werror like the rest of us to get a compiler error instead of a warning.
As for compiler time constants, you certainly can use them for those, but the compiler will happily identify constants without the const keyword, whose true purpose is to cause a build time error if you try to modify it.
Libuutil is a system library that is on any system that uses ZFS, although there are no known external consumers, so if you are interested in being the first, feel free to open bug reports with OpenZFS asking for removed functionality to be restored if you want any of it.
As for compiler time constants, you certainly can use them for those, but the compiler will happily identify constants without the const keyword, whose true purpose is to cause a build time error if you try to modify it.
Regarding libraries, see my other reply:
https://news.ycombinator.com/item?id=42506570
Libuutil is a system library that is on any system that uses ZFS, although there are no known external consumers, so if you are interested in being the first, feel free to open bug reports with OpenZFS asking for removed functionality to be restored if you want any of it.