The arm64 architecture never had a _sysctl system call and therefore
doesn't have a SYS__sysctl define either. Always return UV_ENOSYS.
Fixes: https://github.com/libuv/libuv/issues/2522
PR-URL: https://github.com/libuv/libuv/pull/2524
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>