Old body shop guys would use lead to fill in spots like that,after cleaning it up good by sandblasting..
But big holes would likely need some metal welded in first..
It is becoming a lost art though,not many guys left that know how to do it,and didn't end up dying young from lead exposure and paint fumes,bondo dust..
Most glass shops here just wire brush spots like those and fill them with fiberglass waterproof bondo like Tiger Hair,or "Metal 2 Metal" filler that has a metallic aluminum base when they find rust damage replacing a windshield or back glass..