It's C. I assume the programmer would just be responsible for dealing with dangling pointers and double frees.
Actually, there is. C might be a colossal footgun but reasonably experienced developers do manage to avoid those problems.
Plus..... even if you could do that, WHY? C is a simple language, close to the "metal". If you want a language that has every-feature-and-their-mother, and can be close to the metal when needed, and can be used to blow both your feet off, just use C++.
Adding functional closures to C is somewhat akin to adding "asm" and "volatile" in Haskell.... even if you could do it, why would you? It just breaks the very essence of the language.