make llvm-3.5 the default and remove references to gccApple

make perl be less dumb

revert change to release.nix

pkgs/development/libraries/libunwind/native.nix

@@ -0,0 +1,17 @@
+{ 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;
+}