Help Building GHC on Windows to avoid LGPL

[Edward Z. Yang]

Excerpts from Elliot Cameron's message of 2015-06-30 20:19:40 -0700:
> "inplace/bin/ghc-cabal.exe" check libraries/bytestring
> 'ghc-options: -O2' is rarely needed. Check that it is giving a real benefit and not just imposing longer compile times on your users.
> libraries/bytestring/ghc.mk:4: recipe for target 'libraries/bytestring/dist-install/package-data.mk' failed
> make[1]: *** [libraries/bytestring/dist-install/package-data.mk] Error 1
> Makefile:71: recipe for target 'all' failed
> make: *** [all] Error 2

We fixed this error (it was ghc-cabal not being sufficiently updated to
handle some new Cabal behavior) but I'm surprised your build is failing
because of it, because 7.10.1's shipped Cabal should not be tickling
this bug.

You have a few options:

    1. Try again with a source distribution, since I suspect your
       submodules are not in order, or
    2. Cherry pick 14652b519eca12411e92c28cd06de32612b0973a onto your
       branch, which fixes the bug.

Edward