This will switch to use the clang/C WASM ABI instead of the
wasm_bindgen WASM ABI as of rustc 1.51 (or nightly since [1]),
allowing us to link C and Rust code in a single wasm binary.
[1] https://github.com/rust-lang/rust/pull/79998
Until we get the bindings generation process super stable, let the
bindings get stale with respect to the main repo while still letting
`cargo check` pass.