This commit updates the build script which clones the spec interpreter
for fuzzing to specifically pin at a hardcoded revision. This is
intended at improving reproducibility if we hit any issues while fuzzing
to ensure that the same wasmtime revision is always using the same spec
interpreter revision.
In #3186, we found an issue that requires patching the spec interpreter
for now. Our plan is to have a `fuzzing` branch in our spec-repo mirror
that lets us make these fixes locally before they are upstreamed.
This PR updates the build script for the spec-interpreter wrapper
crate to clone this particular `fuzzing` branch instead of the main
branch.
The WebAssembly spec interpreter is written in OCaml and the new crate
uses `ocaml-interop` along with a small OCaml wrapper to interpret Wasm
modules in-process. The build process for this crate is currently
Linux-specific: it requires several OCaml packages (e.g. `apt install -y
ocaml-nox ocamlbuild`) as well as `make`, `cp`, and `ar`.
