Try to compile C++ library without Emscripten

[grovesNL]

Now that clang supports WebAssembly directly, attempt to compile the C++ SPIRV-Cross library to WebAssembly using --target wasm32-unknown-unknown-wasm and avoid Emscripten.

If this is successful, investigate static linking the Rust and C++ portions together so we can remove the temporary workaround (moving data through JavaScript to call into Emscripten-wasm32 C++ from wasm32 Rust).