libwasm needs tests

[steven-johnson]

AFAICT there are no tests for libwasm -- it's hard to expect external projects to rely on using it without any. Are there plans to add any? (Alternately, plans to have wasm-interp use it instead of the existing api?)

[binji]

There are some examples from the wasm-c-api that are used as basic tests (see https://github.com/WebAssembly/wabt/blob/master/CMakeLists.txt#L570), but I agree, there could be more here.