If you have pits and rock chips, then there really isn't much you could do to fully repair the damage. The best remedy would be to completely replace the windshield. However there are some things you could do to improve slightly at best. For instance there are glass polishes available such as Autoglym Glass Polish that can be used with a buffer. You could give that a try and see if that improves anything.
Here's a link of where you can get it:
http://www.properautocare.com/autglaspol.html
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