If their intention is to support AMD or reward their competitive technological investment, yet they don't need a new processor, then it would be more appropriate to buy AMD stock.
1. It pushes up the price which helps incentivize AMD executives and key employees who have an equity component to their remuneration
2. It makes it easier/cheaper for AMD to raise funding via equity or equity linked markets if they ever need to
At scale, either or both of those could help them though sales might be better