I know it's been answered, but I'd just like to point out it's officially stated that you can on their FAQ:
[Golden Lounge] Can I enter the Golden Lounge at KLIA if I'm travelling on Business Class from an international destination?
May 7, 2018•FAQ
Answer
Business class passengers may enter the Golden Lounge at KLIA under these conditions:-
All passengers holding First and Business class ticket
- Enrich Platinum or Gold cards
Note: Domestic and regional lounge passengers are allowed to utilize the lounge upon departure only. International lounge passengers are allowed to utilise the lounge for departure, transit and arrival.