There are truly readonly data in the physical world, such as ROM. If a value of type `T` is stored in ROM, what's the type of `&T`? It's `const T *`. How to model this in Nim?
If we need to define a callback function (type of a param is `const T *`) in Nim, using ABI would not help. P.S. It's weird that my PR using raw `const` fails to pass t8967 on MacOS/clang, while your PR using `NIM_CONST` succeeds. This is magic. Is it compiled as `C++`? P.P.S. I just found that Nim uses `-w` option when invoking `gcc`. In my projects for embedded systems, `gcc` is invoked in `makefile`, and I am enjoying those warnings, :)
