You'd have to have a LOT of salt per gram of water to significantly (greater than 1C increase.
Using some math you learn in high school chemistry, you can actually calculate the change deltaT=iKm, where deltaT is the increase in temperature, K is the molal boiling point in degC*kg/mol (0.51 for water), and m is the molality in mol/kg, you'll find that 1 mole of sodium chloride (table salt, 58.44 g = 1 mol, which is a lot of salt) and 2 liters of water will have an increase of 0.5 degC.
And regardless, it's largely irrelevant. You gain nothing by 'bulk processing' seawater to make drinkable water through distillation. It takes a little more energy than boiling fresh water, but there is still a linear increase in energy requirement to go from 1 gal to 100 gal. That's to say nothing of energy expenditure of gathering fuel, pollution, effects of cutting down trees, energy loss to the environment when you're boiling....