Fix various c23 compile errors

[reshke]

There are several types of adjustments needed for >= C23.

1. . Replacing an unprototyped function pointer with a prototyped function pointer

      |                                                    _Bool (*)(Node *, sanity_result_t *)
../../../src/include/optimizer/walkers.h:36:49: note: expected ‘_Bool (*)(void)’ but argument is of type ‘_Bool (*)(Node *, sanity_result_t *)’
   36 | extern bool plan_tree_walker(Node *node, bool (*walker) (), void *context, bool recurse_into_subplans);
      |                                          ~~~~~~~^~~~~~~~~~
cdbllize.c:1440:1: note: ‘motion_sanity_walker’ declared here
 1440 | motion_sanity_walker(Node *node, sanity_result_t *result)
      | ^~~~~~~~~~~~~~~~~~~~
cdbllize.c:1550:52: error: passing argument 2 of ‘plan_tree_walker’ from incompatible pointer type [-Wincompatible-pointer-types]
 1550 |                         if (plan_tree_walker(node, motion_sanity_walker, result, true))
      |                                                    ^~~~~~~~~~~~~~~~~~~~
      |                                                    |
      |                                                    _Bool (*)(Node *, sanity_result_t *)
../../../src/include/optimizer/walkers.h:36:49: note: expected ‘_Bool (*)(void)’ but argument is of type ‘_Bool (*)(Node *, sanity_result_t *)’
   36 | extern bool plan_tree_walker(Node *node, bool (*walker) (), void *context, bool recurse_into_subplans);
      |                                          ~~~~~~~^~~~~~~~~~
cdbllize.c:1440:1: note: ‘motion_sanity_walker’ declared here
 1440 | motion_sanity_walker(Node *node, sanity_result_t *result)

I used proxy-functions approach like this:

static bool
contain_motion_walk_impl(Node *node, contain_motion_walk_context *context)
{
    /* code*/
}

static bool
contain_motion_walk_adapter(Node *node, void *context)
{
    return contain_motion_walk_impl(
        node,
        (contain_motion_walk_context *) context
    );
}

This minimizes diff. there are also others way to resolve this, but this is most nit for my taste

2.) K&R-style function definition removal
with C23 this no longer compiles

static int
get_list(bits, low, high, names, ch, file)
	bitstr_t	*bits;		/* one bit per flag, default=FALSE */
	int			low, high;	/* bounds, impl. offset for bitstr */
	char		*names[];	/* NULL or *[] of names for these elements */
	int			ch;			/* current character being processed */
	FILE		*file;		/* file being read */

3.) several const qualifications added.