Revert "Revert "Merge pull request #9543 from NixOS/staging.post-15.06""

This reverts commit 741bf840da.

This reverts the fallout from reverting the major changes.

pkgs/development/libraries/libunwind/native.nix

@@ -1,17 +0,0 @@
-{ stdenv }:
-
-assert stdenv.isDarwin;
-
-stdenv.mkDerivation {
-  name = "libunwind-native";
-
-  unpackPhase = ":";
-  dontBuild = true;
-
-  installPhase = ''
-    mkdir -p $out/lib
-    cat /usr/lib/system/libunwind.dylib > $out/lib/libunwind.dylib
-  '';
-
-  meta.platforms = stdenv.lib.platforms.darwin;
-}