stdenv-darwin: upgrade a few more things

It's a long build and generally painful to split into smaller commits,
so I apologize for lumping many changes into one commit but this is far
easier.

There are still several outdated parts of the darwin stdenv but these
changes should bring us closer to the goal.

Fixes #18461

pkgs/development/compilers/llvm/3.8/clang/default.nix

@@ -30,12 +30,20 @@ let
       sed -i -e 's/DriverArgs.hasArg(options::OPT_nostdlibinc)/true/' lib/Driver/ToolChains.cpp
     '';
 
+    outputs = [ "out" "python" ];
+
     # Clang expects to find LLVMgold in its own prefix
     # Clang expects to find sanitizer libraries in its own prefix
     postInstall = ''
       ln -sv ${llvm}/lib/LLVMgold.so $out/lib
       ln -sv ${llvm}/lib/clang/${version}/lib $out/lib/clang/${version}/
       ln -sv $out/bin/clang $out/bin/cpp
+
+      mkdir -p $python/bin $python/share/clang/
+      mv $out/bin/{git-clang-format,scan-view,set-xcode-analyzer} $python/bin
+      mv $out/share/clang/*.py $python/share/clang
+
+      rm $out/bin/c-index-test
     '';
 
     enableParallelBuilding = true;