cgen: fix sumtype with embedded struct of option field (fix #22984) (#22996)

vlib/v/gen/c/cgen.v

@@ -6963,7 +6963,7 @@ fn (mut g Gen) write_types(symbols []&ast.TypeSymbol) {
 				if sym.info.fields.len > 0 {
 					g.writeln('\t// pointers to common sumtype fields')
 					for field in sym.info.fields {
-						g.type_definitions.writeln('\t${g.styp(field.typ.ref())} ${c_name(field.name)};')
+						g.type_definitions.writeln('\t${g.styp(field.typ)}* ${c_name(field.name)};')
 					}
 				}
 				g.type_definitions.writeln('};')

vlib/v/tests/sumtypes/sumtype_with_embedded_struct_of_option_field_test.v

@@ -0,0 +1,30 @@
+struct Value {
+	x int
+}
+
+struct BValue {
+	v ?Value
+}
+
+struct Word {
+	BValue
+}
+
+struct Long {
+	BValue
+}
+
+struct Variadic {
+	BValue
+}
+
+type Param = Word | Long | Variadic
+
+fn test_sumtype_with_embedded_struct_of_option_field() {
+	a := [Param(Word{}), Long{}, Variadic{}]
+	dump(a)
+	f := a[0]
+	v := f.v
+	dump(v)
+	assert v == none
+}