Implemented parameter passing for function pointers

tests/programs/function-pointer-field.q

@@ -7,10 +7,10 @@ struct Struct {
 main() {
 	s := new(Struct)
 	s.func = f
-	s.func()
+	s.func(0)
 	sys.exit(1)
 }
 
-f() {
-	sys.exit(0)
+f(code int) {
+	sys.exit(code)
 }