enabled and fixed -Wmissing-prototypes compiler warnings

Co-authored-by: matt335672 <30179339+matt335672@users.noreply.github.com>

tests/common/test_list_calls.c

@@ -147,10 +147,6 @@ START_TEST(test_list__simple_strdup_multi)
 }
 END_TEST
 
-int
-split_string_append_fragment(const char **start, const char *end,
-                             struct list *list);
-
 START_TEST(test_list__append_fragment)
 {
     struct list *l = list_create();