Doing non-trivial preprocessing is a mistake. You get slow compilation, hard to debug code, opaque and fragile code, and incredible complexity. If you want metaprogramming, you're better off with C++ it you need C header compatibility, or zig if you don't.
Otherwise, it's probably a good idea to pretend that the only preprocessing directive is #include. With constexpr, even #define is obsolescent.
Otherwise, it's probably a good idea to pretend that the only preprocessing directive is #include. With constexpr, even #define is obsolescent.