This works around a crash (only on OS X for some reason?) where the GHCi
GMP uses the systems memory allocator. We should fix this properly, by
making ghci run constructor functions.

The gcdInt function in the base package now calls gcdInteger with
two small integers. With this weak, the optimiser generates a base
gcdInt that directly calls the gcdInt# primop from this package.
This means there should be no additional overhead compared to when
the base gcdInt called the gcdInt# primop directly.

Moved here from the rts.

This works around haddock not exporting docs across package boundaries

This fixes most of the performance regression in these functions
between 6.8.3 and 6.10.1, it was due to a slight difference in the
strictness between the old and new versions (see comments for
details).  There's still a few percent loss in performance in the div
test in nofib/spectral/integer that I haven't tracked down as yet.

This means that we can export the constructors, but still keep the
GHC.Integer interface generic.

if on a 32-bit machine