FFI changes to support the GHC WASM/WASI backend

[amesgen]

This fixes compilation with the new WASM/WASI backend in GHC 9.6 with an approach as in https://github.com/haskell/time/pull/209.

• WASI does not support process/thread CPU time: https://github.com/WebAssembly/wasi-libc/issues/266
• Due to the way how wasi-libc defines the clock IDs, hsc2hs's #const does not work, hence replacing it with CApiFFI.

I have only compiled this for x86_64-linux and wasm32-wasi; it might make sense to first add CI for Windows/macOS/etc. before merging this to ensure it does not break on those systems.

[CetinSert]

@amesgen – do we need a hackage release?

[amesgen]

That would be neat! As mentioned in the PR description, CI for macOS/Windows (or even more systems) might be neat before releasing this PR. I can create a PR for that if you want.

[CetinSert]

I can create a PR for that if you want.

@amesgen – please do so 😃!

[georgefst]

@amesgen – do we need a hackage release?

With #86 merged, is there anything blocking a release?

[CetinSert]

@georgefst @amesgen

See:

• https://hackage.haskell.org/package/clock-0.8.4
• https://github.com/corsis/clock/releases/tag/0.8.4