Walgreens is based off Illinois, so it's not surprise they're antigun.
Geographic home office location is not the basis for being anti-gun. National pharmacy chains are based in a variety of states and whether the state is pro-gun or not does not have any determination on whether the chain is. You would be hard pressed to find any national, regional, and not many local corporate chains (be it pharmacy or otherwise) that allow employees to carry. Even most or all "pro-gun" sporting goods chains don't allow employees to carry.