Add a crate to interface with the WebAssembly spec interpreter

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`.

crates/fuzzing/wasm-spec-interpreter/src/without_library.rs

@@ -0,0 +1,17 @@
+//! Panic when interpreting WebAssembly modules; see the rationale for this in
+//! `lib.rs`.
+//!
+//! ```should_panic
+//! # use wasm_spec_interpreter::interpret;
+//! let _ = interpret(&[], vec![]);
+//! ```
+
+use crate::Value;
+
+#[allow(dead_code)]
+pub fn interpret(_module: &[u8], _parameters: Vec<Value>) -> Result<Vec<Value>, String> {
+    panic!(
+        "wasm-spec-interpreter was built without its Rust-to-OCaml shim \
+        library; re-compile with the dependencies listed in its README.md."
+    );
+}