Rinse giblets and neck. Wrap liver airtight and chill to add later, or save for other uses.
In a 5- to 6-quart pan over high heat, combine giblets, neck, 10 cups broth, wine, onions, carrots, celery, parsley, and marjoram. Cover and bring to a boil. Reduce heat and simmer until gizzard is very tender when pierced, about 1 1/2 hours. If desired, add the liver and simmer 10 more minutes.
Meanwhile, in a 10- to 12-inch frying pan over high heat, stir flour until it's golden brown and smells richly toasted (but not scorched), 12 to 15 minutes. Pour into a bowl.
Pour broth through a fine strainer into a bowl. Discard vegetables. Measure broth. If you have more than 8 cups, boil to reduce; if you have less, add more chicken broth.
Pull meat off neck; discard bones. Finely chop meat and giblets (optional).
With a whisk, smoothly mix about 3 cups of the simmered broth into flour. Pour into the 5- to 6-quart pan and add remaining broth. If desired, scrape turkey drippings free from roasting or barbecue drip pan and add to broth. Stir over high heat until boiling, then reduce heat and simmer, stirring often, for about 5 minutes. Add giblets, if desired, and stir 1 to 2 minutes more. Pour into a bowl. Add salt and pepper to taste.