fix avx destection

The OS is able to disable avx. In that case our avx detection is wrong.
See xmrig issue: https://github.com/xmrig/xmrig/issues/951

Import fix: https://github.com/xmrig/xmrig/commit/6052da3c4399514c95245b2d342f04baa20958db#diff-92fa29935c136762d35981769ac79f52

thx @xmrig for the notification.