Add -fworker-wrapper flag which enables the worker-wrapper transformation.
It is implied by -O.
The expected users of this flag, which includes myself, are GHC API users.
In my Haskell-to-Hardware compiler, which uses the GHC API, I have seen
no benifits of the worker-wrapper transformation. It does however induce
longer compilation times.
Further discussion can be seen here:
https://mail.haskell.org/pipermail/ghc-devs/2015-October/010096.html