Compile with clang and wasm32-wasi target by using the wasi-sdk version 20

Install wasi-sdk and then set WASI_SDK_PATH to the root of the install.

You can then rebuild the wasm for the tests by running:

make CC=${WASI_SDK_PATH}/bin/clang SYSROOT=${WASI_SDK_PATH}/share/wasi-sysroot

If you update the version of the wasi-sdk to be used for the compile remove all of the *.wasm files in the wasm directory to ensure you rebuild/test all of the tests with the new version.