While garlic is not inherently gluten-free, you will be able to purchase it at the store with no gluten in it. Organic grocery stores will most likely be able to accommodate your needs, so make sure you take the time to look around for garlic that has no gluten it in whatsoever.
Usually you will be able to tell from the packaging whether or not it has gluten in it. Some people have a gluten allergy which does not allow them to tolerate it. If you have this type of allergy, it is highly recommended that you search for a gluten-free type of garlic at the supermarket.