Better to be loud that we don't support attaching arbitrary host info to `externref`s than to limp along and pretend we do support it. Supporting it properly won't reuse any of this code anyways.
This is the wasmtime-wast crate, which contains an implementation of WebAssembly's
"wast" test scripting language, which is used in the
WebAssembly spec testsuite, using wasmtime for execution.