IMO you should not workout when legitimately sick. Some will disagree and point to the "man up and lift" mentality but in the long run you are much, much better off.
When sick your body needs to have full force and energy expenditure going towards fighting off the illness and becoming healthy. If you interfere with this process (by putting additional stress on your body) you will only further worsen your bodies fight/healing process.
Furthermore you won't be training at 100% and recovery will be way below normal status making the workout itself almost useless.
Recover, then go train.