haskell-Southpaw cannot be built on Unix.

pkgs/development/haskell-modules/configuration-common.nix

@@ -870,6 +870,7 @@ self: super: {
   # This package can't be built on non-Windows systems.
   Win32 = overrideCabal super.Win32 (drv: { broken = !pkgs.stdenv.isCygwin; });
   inline-c-win32 = dontDistribute super.inline-c-win32;
+  Southpaw = dontDistribute super.Southpaw;
 
   # Doesn't work with recent versions of mtl.
   cron-compat = markBroken super.cron-compat;