It would take either a Supreme Court ruling or an amendment to the constitution to define "natural born citizen" as it relates to eligibility for presidency.
Some contend that being born to parents who are U.S. citizens regardless of location qualifies. Others contend that is not what the founding fathers intended... or at the very least they were not specific enough around this scenario that anyone can say for certain.
Funny though how aggressive the "birthers" were in their attempts to label Obama as ineligible. There doesn't seem to be the same fervor when it comes to Cruz. And there is zero doubt that he was born on foreign soil.