42acb72c54
To avoid the large download size of the spec repository mentioned [here](https://github.com/bytecodealliance/wasmtime/pull/3124#discussion_r684605984), this change removes it as a submodule and instead clones it shallowly when the directory is empty (or not present) when `build.rs` is run.
This directory contains the necessary parts for building a library with FFI access to the Wasm spec interpreter. Its major parts:
spec: the Wasm spec code as a Git submodule (you may need to retrieve it: `git clone https://github.com/bytecodealliance/wasm-spec-mirror).interpret.ml: a shim layer for calling the Wasm spec code and exposing it for FFI accessMakefile: the steps for gluing these pieces together into a static library