Compiler assertion when defining a function with return type untyped_list #2368. In general, improve error message when ct types are return types.

test/test_suite/compile_time/untyped_list_rtype.c3

@@ -0,0 +1,18 @@
+
+
+macro $typeof({}) foo2() { return {}; }
+
+struct Foo
+{
+    int a;
+}
+
+fn $typeof(Foo.a) foo3() {} // #error: may not return a member reference
+
+fn $typeof({}) foo() {} // #error: A function may not return an untyped list
+
+fn int main()
+{
+	foo2();
+	return 0;
+}