tests: add empty_struct_compare_test.v too (#17270)

vlib/v/tests/empty_struct_compare_test.v

@@ -0,0 +1,39 @@
+type MyInt = int
+type MyOptInt = ?int
+type MyOptStr = ?string
+type MySumType = f64 | int | string
+
+struct Foo {
+	i            int
+	i_opt        ?int
+	arr          []int
+	arr2         []int = [1, 2]
+	dec          f64
+	dec_opt      ?f64
+	dec_arr      []f64
+	i_arr        []int
+	str_arr      []string
+	opt_int      ?int
+	opt_int2     ?int = 3
+	myalias      MyInt
+	myoptlias    ?MyInt
+	myoptlias2   ?MyInt = MyInt(1)
+	myoptint     MyOptInt
+	mysumtype    MySumType
+	mysumtypeopt ?MySumType
+	str          string
+	str2         string = 'b'
+	str_opt      ?string
+	str_opt2     ?string = 'a'
+	str3         MyOptStr
+}
+
+struct Bar {
+pub:
+	foo ?Foo = none
+}
+
+fn test_main() {
+	m := Bar{}
+	assert m == Bar{}
+}