claying the windshield will certainly help; claying obviously cannot cure pitting but will help remove the many minor particles that remain stuck to the windshield.
I recently applied a coat of Jet Seal 109 to my windshield and was surprised at the improvement. I had been reluctant to use a sealant on the windshield, on the theory that adding anything to the windshield would reduce optical clarity. I was surprised that JS 109 actually improved clarity, and reduced the visibility of the small scratches that are most evident when driving into the sun. I did not notice any smearing or streaking, or any effect of the sealant at all, other than improving clarity. This may not work as well for pitting, but it certainly worked on improving the effects of small scratches in this case. Naturally a sealant should be added only after a thorough washing and claying.
I would be reluctant to use a machine polisher on a windshield unless you are really confident with it. The goal of machine polishing is to remove some of the clear coat that is on top of the paint layer; I don't believe that the windshield also has this clear coat, although please correct me if I'm mistaken. It may work out fine, I would just check it out thoroughly first.