cgen: fix map clone (#7366)

vlib/builtin/map_test.v

@@ -426,3 +426,17 @@ fn test_modify_map_value() {
 	assert m1['foo'] == 8
 	assert m1['bar'] == 14
 }
+
+fn test_map_clone() {
+	mut nums := {
+		'foo': 1,
+		'bar': 2
+	}
+	mut nums2 := nums.clone()
+	nums2['foo']++
+	nums2['bar'] *= 4
+	assert nums['foo'] == 1
+	assert nums['bar'] == 2
+	assert nums2['foo'] == 2
+	assert nums2['bar'] == 8
+}