ported rewrite2 to c3

test/test_union.c3

@@ -0,0 +1,26 @@
+
+struct CmdA {
+	int a, b;
+}
+
+struct CmdB {
+	float a, b;
+}
+
+union AnyCmd {
+	CmdA a;
+	CmdB b;
+}
+
+struct Cmd {
+	int type;
+	AnyCmd cmd;
+}
+
+fn int main()
+{
+	Cmd c;
+	c.type = 1;
+	c.cmd.a = {.a = 1, .b = 2};
+	return 0;
+}