Build error with wasm32-wasi: system `wasi' not recognized

I'm trying to build `unix` with `wasm32-wasi-cabal` using my new [`ghc-wasm-backend` Docker image](https://hub.docker.com/repository/docker/brandonchinn178/ghc-wasm-backend/general), and I'm getting this error:
```
checking host system type... Invalid configuration `wasm32-wasi': system `wasi' not recognized
configure: error: /bin/bash //tmp/cabal-install.-10744/dist-newstyle/tmp/src-10745/unix-2.8.0.0/config.sub wasm32-wasi failed
```
Any idea what's wrong?

Repro:
1. `docker pull brandonchinn178/ghc-wasm-backend:2b62739d7e6cc65f444029f252578f2dddb95ce3`
2. `docker run --rm -it --entrypoint bash brandonchinn178/ghc-wasm-backend:2b62739d7e6cc65f444029f252578f2dddb95ce3`
3. `wasm32-wasi-cabal update`
4. `wasm32-wasi-cabal install ormolu --allow-newer='template-haskell' --allow-newer=base --allow-newer=ghc-prim --allow-newer=unix` (or install some other library depending on unix)