Partition all-cabal-hashes into case-insensitive-safe components.

OS X by default has a case-insensitive filesystem, and fetching
all-cabal-hashes there fails due to a hash mismatch caused by package
pairs like compactable and Compactable. This partitions the package set
such that each partition contains no equivalent-up-to-case pairs.

pkgs/data/misc/hackage/default.nix

@@ -1,11 +1,33 @@
-{ fetchFromGitHub }:
+{ fetchFromGitHub
+, stdenv
+, pkgconfig
+, libarchive
+, glib
+, # Override this to use a different revision
+  src-spec ?
+    { owner = "commercialhaskell";
+      repo = "all-cabal-hashes";
+      rev = "901c2522e6797270f5ded4495b1a529e6c16ef45";
+      sha256 = "05jmwsgrk77nz9vvgfbpsps0l320qgjpkr2c9zhkn9sc3d275lfb";
+    }
+, lib
+}:
 
 # Use builtins.fetchTarball "https://github.com/commercialhaskell/all-cabal-hashes/archive/hackage.tar.gz"
 # instead if you want the latest Hackage automatically at the price of frequent re-downloads.
-
-fetchFromGitHub {
-  owner = "commercialhaskell";
-  repo = "all-cabal-hashes";
-  rev = "901c2522e6797270f5ded4495b1a529e6c16ef45";
-  sha256 = "0wng314y3yn6bbwa5ar254l7p8y99gsvm8ll4z7f3wg77v5fzish";
-}
+let partition-all-cabal-hashes = stdenv.mkDerivation
+      { name = "partition-all-cabal-hashes";
+        src = ./partition-all-cabal-hashes.c;
+        unpackPhase = "true";
+        buildInputs = [ pkgconfig libarchive glib ];
+        buildPhase =
+          "cc -O3 $(pkg-config --cflags --libs libarchive glib-2.0) $src -o partition-all-cabal-hashes";
+        installPhase =
+          ''
+            mkdir -p $out/bin
+            install -m755 partition-all-cabal-hashes $out/bin
+          '';
+      };
+in fetchFromGitHub (src-spec //
+  { postFetch = "${partition-all-cabal-hashes}/bin/partition-all-cabal-hashes $downloadedFile $out";
+  })