getExecutablePath doesn't work on wasm backend

On wasm32, getExecutablePath returns only the wasm module's filename (e.g. foo.wasm). This makes perfect sense since the information is only available via argv[0], which wasmtime will not leak any host filesystem info into, and in the virtual filesystem (if it's provided) there may not even exist foo.wasm at all. Consequently, executablePath returns Nothing.

This may still be surprising to new users of the wasm backend, whose user program relies on getExecutablePath/executablePath being able to fetch the program's absolute path. So, this ticket serves as a placeholder so the disabled test (executablePath) can point to.