Official KB article 3021976.
Compiler and CRT
The VS 2013 Update 5 includes a new version of the C++ compiler (18.00.40629.0). There's no new C/C++ Runtime--it still uses CRT version 12.0.21005.1 from VS 2013 RTM--, but there are updated remote debugging tools packages.
Windows 10: VS 2013 Update 5 will enable the Graphics Tools optional feature required to use the Direct3D debug device on Windows 10. See this post for details.
DirectX SDK: If you need to continue to make use of legacy DirectX SDK components such as D3DX9, D3DX10, D3DX11, or XAudio 2.7 with Visual Studio 2013, see MSDN for details on mixing the paths correctly. See also DirectX SDKs of a certain age, The Zombie DirectX SDK, Living without D3DX, DirectX SDK Tools Catalog, and DirectX SDK Samples Catalog