I was trying an alternative solution. I think you may be able to fix the problems this approach has with not quite being semantically identical to a "for" block, but I couldn't overcome the restrictions on not being able to declare another variable.

You could possibly wrap up the "compare elephant and head, except the first time, then just return true" logic into a function with a static variable in, but it would mean the code would be definitely non-reentrant. (Unless your preprocessor did something clever with the LINE directive in the macro, but I can't remember, that wasn't in C90 either, right?)