GMP extras should be forked off into a separate package

[treeowl]

You could make an integer-gmp-bits package for this. Once GHC Trac #7860 gets fixed, that can turn into a thin shell.

[superbobry]

The whole extras thing is a bit tricky. It was written for the older integer-gmp and does not even compile with integer-gmp2. So I guess we have a rewrite to do as well...

Update: the last GHC version to ship integer-gmp by default is broken anyway.