The script addition is a bit hacky, but there's no obvious straightforward arch/version-independent way to get most of the build path. And eventually, once issues with HLS etc. are sorted out we will revert to using Cabal hooks anyway.
We drop the tools specifically designed for Haskell and Rust together, in favour of general tools for using each with C.
Namely, we use Mozilla's `cbindgen` for generating header files from the Rust source, and Well-Typed's new `hs-bindgen` tool for generating Haskell from those header files.
The Rust code here is essentially the result of expanding the old macro, then inlining and renaming internals.
The most important thing here is that we're now relying solely on robust well-maintained tools.
