Just Googled PVC+hydrogen chloride gas. All most of the search results were from questionable sources. I know that Google is a VERY shallow info pool and it showed. I also looked into the (M)SDS for PVC pipe and found information about HCL gas and found that seems to happen when PCV is burned, nothing about when it gets heated, only when burned. The gas is just a part the combustion process. Per the CDC, Hydrogen Chloride gas has a pungent odor.
FWIW The times that I heated foam core PVC I did not notice any odor at all.