integer-gmp-1.1 should be uploaded to Hackage
The latest release currently available on Hackage is v1.0.3.0: http://hackage.haskell.org/package/integer-gmp-1.0.3.0
EDIT: For (my) future reference, the haddocks of integer-gmp-1.1
are available at http://downloads.haskell.org/~ghc/9.0.1/docs/html/libraries/integer-gmp-1.1/GHC-Integer-GMP-Internals.html.