patch 8.2.3320: some local functions are not static

Problem:    Some local functions are not static.
Solution:   Add "static".  Move snprintf() related code to strings.c.
            (Yegappan Lakshmanan, closes #8734)

src/list.c

@@ -620,7 +620,7 @@ list_append_tv(list_T *l, typval_T *tv)
  * As list_append_tv() but move the value instead of copying it.
  * Return FAIL when out of memory.
  */
-    int
+    static int
 list_append_tv_move(list_T *l, typval_T *tv)
 {
     listitem_T	*li = listitem_alloc();