That's where the labeling laws have come in handy. HFCS is listed for those who wish to avoid it. Gluten has been on the label for a long time and in the last five(?) years (I am certain of the last 3 years) voluntary labeling of "gluten/wheat free" has appeared all over the place and stating when a product is manufactured in a place where gluten exists.

My uncertainty arises in regards to time because I only started paying attention when a coven mate appeared who is gluten allergic.