Condition java sim build on -PmakeSim flag
Condition java sim build on -PmakeSim flag

This prevents issues building wpilib if you have ntcore but haven't
built desktop
If you want to build sim, use -PmakeSim
This will require the desktop build of ntcore, which can be done with:
./gradlew build publish -PmakeDesktop

Change-Id: I20f379267a226dbdfcff8fe6223670257725965a

PatrickPenguinTurtle/allwpilib,PeterMitrano/allwpilib,PeterMitrano/allwpilib,JLLeitschuh/allwpilib,JLLeitschuh/allwpilib,333fred/allwpilib,RAR1741/wpilib,PatrickPenguinTurtle/allwpilib,PatrickPenguinTurtle/allwpilib,robotdotnet/allwpilib,robotdotnet/allwpilib,RAR1741/wpilib,JLLeitschuh/allwpilib,robotdotnet/allwpilib,PatrickPenguinTurtle/allwpilib,PatrickPenguinTurtle/allwpilib,PatrickPenguinTurtle/allwpilib,RAR1741/wpilib,PatrickPenguinTurtle/allwpilib,JLLeitschuh/allwpilib,robotdotnet/allwpilib,PeterMitrano/allwpilib,333fred/allwpilib,PeterMitrano/allwpilib,333fred/allwpilib,JLLeitschuh/allwpilib,333fred/allwpilib,JLLeitschuh/allwpilib,RAR1741/wpilib,robotdotnet/allwpilib,RAR1741/wpilib,RAR1741/wpilib,333fred/allwpilib,PeterMitrano/allwpilib,333fred/allwpilib,robotdotnet/allwpilib,PeterMitrano/allwpilib,PeterMitrano/allwpilib,RAR1741/wpilib,JLLeitschuh/allwpilib