Jcardinez, the rule about those diseases is very strict in Libya, when they find out about it, you will lose your job on the spot and be asked to leave the country. There is no way to avoid the medical checks as most employers only accept recent Libyan medical certificates, some even choose which hospital you should go to.
I think you're taking a big risk accepting a job in Libya, they will NOT give you residence permit (iqama) and they will not even keep you as an employee.