Using the BuildGraph to create an installed binary build of the Engine will fail if Simplygon is not installed.

A user reported that attempting to create an installed binary build of the Engine using BuildGraph will fail. This seems to be because we include the UE Simplygon implementation, but do not disable building it if Simplygon is not installed.

When the build fails, the following errors are shown:

Module.SimplygonSwarm.cpp
D:\Source\ForTestingPurposes\UnrealEngine-master\Engine\Source\Developer\SimplygonSwarm\Public\SimplygonSwarmPrivatePCH.h(12): fatal error C1083: Cannot open include file: 'ssf.h': No such file or directory

Error executing C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin\amd64\cl.exe (tool returned code: 2)

Module.SimplygonMeshReduction.cpp
D:\Source\ForTestingPurposes\UnrealEngine-master\Engine\Source\Developer\SimplygonMeshReduction\Public\SimplygonTypes.h(9): fatal error C1083: Cannot open include file: 'SimplygonSDK.h': No such file or directory

Error executing C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin\amd64\cl.exe (tool returned code: 2)

1. Make sure Simplygon is not installed.
2. Download Master branch source code as a zip file from GitHub.
3. Unzip the source code.
4. Run Setup.bat
5. Run GenerateProjectFiles.bat
6. Open the UE4.sln file in Visual Studio and build the AutomationTool.
   • Development Editor, Win64
7. In Windows Explorer, navigate to the folder where the AutomationTool.exe file is located.
   • Engine\Binaries\DotNET
8. Without any files or folders selected, hold the Shift key and right-click on an empty space in the Windows Explorer window.
9. Select the "Open command window here" option.
10. In the command window that opens, enter the following command: AutomationTool BuildGraph -target="Make Installed Build Win64" -script=Engine/Build/InstalledEngineBuild.xml -clean -set:HostPlatformOnly=true

RESULT:
The build fails with the errors mentioned in the description.

EXPECTED:
The build completes successfully.

WORKAROUND:
Deleting the SimplygonSwarm and SimplygonMeshReduction folders from Engine/Source/Developer may allow the build to complete successfully.