add_action('woocommerce_product_query', 'custom_product_query');
function custom_product_query($q)
{
    if (!$q->is_main_query()) return;
    $q->set('meta_query', array(
        'relation' => 'OR',
        array(
            'key' => '_stock_status',
            'value' => 'instock',
            'compare' => '=',
        ),
        array(
            'key' => '_stock_status',
            'value' => 'outofstock',
            'compare' => '=',
        ),
    ));
    $q->set('orderby', 'meta_value');
    $q->set('order', 'ASC');
}