[Nix-dev] ghc wrapper

[Peter Simons]

Hi Karn,

 > The attached patch allows for the change in the package database flag
 > in GHC 7.6.1 (from package-conf to package-db). The change in flag
 > combined with the -Werror option was causing build failures.

that patch is rather intrusive, because it causes re-builds of all
Haskell packages with all compilers on all platforms.

I have a similar patch that tries to accomplish the same thing without
affecting non-GHC-7.6.1 packages, but it needs more testing before I can
commit it. I'll probably open a pull request on Github soon so that
others can test it, too.

Take care,
Peter