{% assign reorder_url = "" %}
  {% for line_item in order.line_items %}
    {% capture reorder_url %}{{ reorder_url | append: line_item.variant_id | append: ':' | append: line_item.quantity | append: ',' }}{% endcapture %}
{% endfor %}
<a href="{{ '/cart/' | append: reorder_url }}" class="btn">reorder</a></td>