From my understanding of the issue, a scripting language was once a small language with one purpose which quickly expanded to fill all possible needs (e.g. Perl).
By this definition C isn't a scripting language, as it was small and stood that way.
I'm definitely stealing from someone else's comment a long time ago but they said it very well: The difference is that scripting languages have no main function (as far as I know).
C is a general-purpose programming language but I don't think anyone ever called it a "scripting" language... (besides "scripting" DSL's with C syntax in some games)
By this definition C isn't a scripting language, as it was small and stood that way.