For whiteboard coding, I've always given interviewees their choice of programming language and have said, "Don't worry about syntax." For me it's more about how you approach the problem than whether you can spell correctly.
I code in a variety of languages and every time I use .indexOf(), I can't remember if it's (needle, haystack) or (haystack, needle). Of course, my IDE shows me the correct way and I go with it in 0.3 seconds.
On a whiteboard, if I were marked down for getting that the "wrong", I don't think I'd like to work for those kind of people anyway. I have no interest in memorizing the exact syntax of every standard library call in every language. When I can look it up almost instantaneously, my mental efforts are best spent elsewhere.