RAII is just automation and semantic sugar for something like this (or the equivalent set of goto labels that do the freeing at the end of the function):

    {
      void *buffer = malloc(SIZE_MAX);
      if (buffer) {
        if (!do_stuff(buffer)) {
          free(buffer);
          return;
        }
        more_stuff(buffer);
        free(buffer);
      }
      return;
    }

If you wanted something like that in C it doesn't need to emulate C++ style RAII with classes and strongly typed constructors. It could look like something like, for example, where you just define pairs of allocator and free functions:

    allocdef void *autobuffer(malloc, free);
    ...
    {
      autobuffer buffer(SIZE_MAX);

      if (buffer) {
        if (do_stuff(buffer)) {
          return;
        }
        more_stuff(buffer);
      }
      return;
    }

The implementation would effectively be a Lisp style macro expansion encoded in the C compiler (or preprocessor) that would just basically write out the equivalent of the first listing above.