Originally I had thought that these weren't used by head.hackage has shown otherwise:

• gcdExtInteger :: Integer -> Integer -> (# Integer, Integer #)
• powModSecInteger :: Integer -> Integer -> Integer -> Integer
• powModInteger :: Integer -> Integer -> Integer -> Integer
• recipModInteger :: Integer -> Integer -> Integer
• nextPrimeInteger :: Integer -> Integer
• testPrimeInteger :: Integer -> Int# -> Int#

It's a bit unclear how many of these we really want to support in ghc-bignum. Some seem awfully specialised. Nevertheless, they are all appear to be used (or at least wrapped) by cryptonite