builtin: support also [abc,def].sort(b>a)

vlib/builtin/string.v

@@ -1014,6 +1014,16 @@ pub fn compare_strings(a, b &string) int {
 	return 0
 }
 
+fn compare_strings_reverse(a, b &string) int {
+	if a.lt(b) {
+		return 1
+	}
+	if a.gt(b) {
+		return -1
+	}
+	return 0
+}
+
 fn compare_strings_by_len(a, b &string) int {
 	if a.len < b.len {
 		return -1

vlib/builtin/string_test.v

@@ -99,6 +99,19 @@ fn test_sort() {
 	assert vals[3] == 'arr'
 }
 
+fn test_sort_reverse() {
+	mut vals := [
+		'arr', 'an', 'a', 'any'
+	]
+	len := vals.len
+	vals.sort(b>a)
+	assert len == vals.len
+	assert vals[3] == 'a'
+	assert vals[2] == 'an'
+	assert vals[1] == 'any'
+	assert vals[0] == 'arr'
+}
+
 fn test_split_nth() {
 	a := "1,2,3"
 	assert (a.split(',').len == 3)