In a 5- to 6-qt. pan over high heat, combine giblets, neck, 10 cups broth, the wine, onions, carrots, celery, parsley, marjoram, and 1 tsp. each salt and pepper. Cover and bring to a boil. Reduce heat and simmer until all giblets are very tender when pierced, about 1 hour.
Toast flour in a large frying pan over medium-high heat, stirring, until deep 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, reserving pan. Discard vegetables (save giblets and neck if you like). Measure broth. If you have more than 8 cups, boil to reduce; if you have less, add more chicken broth.
If using giblets and neck, pull meat off neck; discard bones. Finely chop meat and giblets.
Whisk about 3 cups simmered broth into flour. Pour into the 5- to 6-qt. pan and add remaining broth.
Scrape drippings free from roasting or grill drip pan; add to broth. Bring to a boil over high heat, stirring; lower heat and simmer, stirring often, about 5 minutes. Add giblets, if you like, and stir 1 to 2 minutes more. Season with salt and pepper to taste.
Make ahead: Up to 1 day ahead, make through Step 5, cover, and chill. To reheat, add turkey drippings and warm over low heat, stirring often.
Note: Nutritional analysis is per 1/3-cup serving.