Implement a function to return the error code of a wasi_trap_t

[fschutt]

Currently if we call wasm_func_call on the _start function, we need to have a way to check whether the exit code exited with 0, as it's currently the case for WASI.

own wasm_trap_t *trap = wasm_func_call(start_function, &args, &results);

This should be done in the 3.2.0-beta release so that we can link to the new API in the 3.2.0 release.

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[stale[bot]]

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