Historically, Ghirardelli - which dates to 1852 - has been 100% gluten-free. That changed in June 2008, when the company added the "crisp" flavor to its line of Luxe Milk chocolate squares. The toasted rice used in the crisps contains barley malt. According to customer service, those Milk Chocolate Luxe with Crisps are produced on the same line as the baking bars and squares. In order to reduce cross-contamination risks, the lines are cleaned when changing from one product to the next, and the first two batches of any product are disposed of and not packaged. I would be willing to bet that the chocolate bars and squares remain safely gluten-free, and that the potential for cross-contamination - and especially cross-contamination to a level meaningful to someone with Celiac or gluten-intolerance - is minimal.
If you have concerns, Ghirardelli's baking chips and powdered cocoa are produced on dedicated lines free of any gluten ingredients. (For what it's worth, we use Ghirardelli regularly in our baking, love it, and have never had a problem getting sick. We tend to use their baking chips, not necessarily because they're produced on a dedicated line, but rather because the chips are often less expensive per pound than an equal quantity of the baking bars, and you're getting the exact same chocolate either way.)
Nestle's baking chips, bars and cocoa are sold under its Toll House brand. Nestle's policy is to be very transparent about their ingredients for the sake of consumers with food allergies and other concerns. Consequently, they list potential gluten cross-contaminants (such as barley) in addition to wheat (which is the only gluten ingredient required to be listed under current U.S. food labeling laws). Nestle does maintain an internal gluten-free products list. By the company's own standards, only those products that are free of gluten ingredients AND which are not produced on a shared line or in a shared facility with potential for cross-contamination are listed.
That said, many of their products not strictly listed on that gluten-free list are likely also gluten-free. For example, the entire line of baking chips should be gluten-free, with the exception of the butterscotch chips, which are NOT gluten-free. Similarly, the semi-sweet baking bars should be gluten-free, though they are produced on a shared line with wheat products. Whether or not this constitutes an acceptable cross-contamination risk is up to the individual. Your best bet if considering a Nestle baking product is to review the actual ingredients label, and look for allergen and advisory labeling. Then make your decision.
Finally, there is Baker's, which has been around since the 1700s, and which today is a division of Kraft Foods. To my knowledge, Baker's doesn't have a product in its line that contains gluten, and as such, all of their baking bars should be gluten-free. Frustratingly, however, their customer service department has been unresponsive to my inquiries, so I've been unable to confirm gluten-free status and company policies and protocols for handling ingredients. So I'm afraid I can't give you as insightful an answer for this company, but I can say that, anecdotally, we've used Baker's chocolate without issue in the past.
Happy baking this holiday season!