sort: fix sorting by struct fields

vlib/cli/flag.v

@@ -183,3 +183,10 @@ fn (flags []Flag) contains(name string) bool {
 	return false
 }
 
+
+fn (mut flags []Flag) sort2() {
+       flags.sort_with_compare(fn (a, b &Flag) int {
+               return compare_strings(&a.name, &b.name)
+       })
+}
+