Well, the way most people understood the question many years ago you had to be born here.
The con argument to make Cruz eligible is that he had 1 parent who was a citizen. That wouldn't have been enough for anyone several decades ago. That wasn't enough for them when it came to Obama. And not just the birther nuts. If Obama hadn't been born in Hawaii, a lot more people than birther nuts would have been saying he was excluded. But it's OK for Cruz.
While I personally think the constitutional requirement that presidential candidates be born here is stupid, it's laughable how conservatives contort themselves to get around it when they want to.