I got the same error as well!
[458/464] Link Krieg-OculusInput.lib
[459/464] Link Krieg-ExampleDeviceProfileSelector.lib
[460/464] Link Krieg-CharacterAI.lib
[461/464] Link Krieg-RuntimePhysXCooking.lib
[462/464] Link Krieg-WindowsMoviePlayer.lib
ERROR: UBT ERROR: Failed to produce item: D:\UnrealEngineSource\Engine\Plugins\Media\WmfMedia\Binaries\Win64\Krieg-WmfMedia.lib
Total build time: 1293.23 seconds (Local executor: 0.00 seconds)
My guess is there is an issue loading the Windows Media File plugin when using Visual Studio 2017. As you can see from the 4.20 changelog for Unreal Engine, Visual Studio 2017 is now officially the default VS version for projects:
Core Updates:
Visual Studio 2017. UE4 will now use the Visual Studio 2017 compiler, and generate project files for Visual Studio
2017 by default. We’ve also added support for the Windows 10 SDK.