Add function to build a ghc standalone archive (OSX/iOS only)

pkgs/development/compilers/ghc/head.nix

···
 } // stdenv.lib.optionalAttrs (cross != null) {
   name = "${cross.config}-ghc-${version}";
 
+  patches = [ ./ios-linker.patch ];
+
   preConfigure = commonPreConfigure + ''
-    sed 's|#BuildFlavour  = quick-cross|BuildFlavour  = perf-cross|' mk/build.mk.sample > mk/build.mk
+    sed 's|#BuildFlavour  = quick-cross|BuildFlavour  = quick-cross|' mk/build.mk.sample > mk/build.mk
+    echo "GhcRtsCcOpts = -glldb -Og" >> mk/build.mk
+  '';
+
+  postUnpack = ''
+    mkdir -p $out/nix-support
+    mv $sourceRoot $out/nix-support/source
+    sourceRoot=$out/nix-support/source
   '';
 
   configureFlags = [
···
   buildInputs = commonBuildInputs ++ [ stdenv.ccCross stdenv.binutilsCross ];
 
   dontSetConfigureCross = true;
+
+  dontStrip = true;
 
   passthru = {
     inherit bootPkgs cross;

pkgs/os-specific/darwin/ghc-standalone-archive/default.nix

···
+{ runCommand, cctools }:
+{ haskellPackages, src, deps ? p : [], name }: let
+  inherit (haskellPackages) ghc ghcWithPackages;
+  with-env = ghcWithPackages deps;
+  crossPrefix = if (ghc.cross or null) != null then "${ghc.cross.config}-" else "";
+  ghcName = "${crossPrefix}ghc";
+in runCommand name { buildInputs = [ with-env cctools ]; } ''
+  mkdir -p $out/lib
+  mkdir -p $out/include
+  ${ghcName} ${src} -staticlib -outputdir . -o $out/lib/${name}.a -stubdir $out/include
+  for file in ${ghc}/lib/${ghcName}-${ghc.version}/include/*; do
+    ln -sv $file $out/include
+  done
+''

pkgs/top-level/all-packages.nix

···
   simplenote = callPackage ../applications/misc/simplenote { };
 
   hy = callPackage ../development/interpreters/hy {};
+
+  ghc-standalone-archive = callPackage ../os-specific/darwin/ghc-standalone-archive { inherit (darwin) cctools; };
 }