test: only declare a main() when fuzzing with AFL
test: only declare a main() when fuzzing with AFL

libFuzzer will provide a main(). This also fixes a weak linking
issue when fuzzing with libFuzzer on macOS.


Former-commit-id: ea093a01b004fc692ea614c5da129cb0229f0e94
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin,syscoin/syscoin2,syscoin/syscoin2