merge geant4 changes from root6 branch

[smuzaffar]

No description provided.

[cmsbuild]

A new Pull Request was created by @smuzaffar (Malik Shahzad Muzaffar) for branch IB/CMSSW_10_0_X/gcc630.

@cmsbuild, @smuzaffar, @gudrutis, @mrodozov can you please review it and eventually sign? Thanks.
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[mrodozov]

I think something from here broke the CLANG IBs, not sure yet what exactly. A lib was missing, i tried build it locally which failed with 'undefined reference to some G4 stuff':

tmp/slc6_amd64_gcc630/src/SimG4Core/PhysicsLists/src/SimG4CorePhysicsLists/UrbanMscModel93.o: In function `UrbanMscModel93::ComputeTruePathLengthLimit(G4Track const&, double&)':
/build/mrodozov/CMSSW_10_0_CLANG_X_2017-12-21-2300/src/SimG4Core/PhysicsLists/src/UrbanMscModel93.cc:(.text+0x1881): undefined reference to `G4MTHepRandom::getTheEngine()'
/build/mrodozov/CMSSW_10_0_CLANG_X_2017-12-21-2300/src/SimG4Core/PhysicsLists/src/UrbanMscModel93.cc:(.text+0x188f): undefined reference to `G4MTRandGaussQ::transformQuick(double)'
tmp/slc6_amd64_gcc630/src/SimG4Core/PhysicsLists/src/SimG4CorePhysicsLists/UrbanMscModel93.o: In function `UrbanMscModel93::ComputeGeomPathLength(double)':
/build/mrodozov/CMSSW_10_0_CLANG_X_2017-12-21-2300/src/SimG4Core/PhysicsLists/src/UrbanMscModel93.cc:(.text+0x239f): undefined reference to `G4MTHepRandom::getTheEngine()'
/build/mrodozov/CMSSW_10_0_CLANG_X_2017-12-21-2300/src/SimG4Core/PhysicsLists/src/UrbanMscModel93.cc:(.text+0x2481): undefined reference to `G4MTHepRandom::getTheEngine()'
/build/mrodozov/CMSSW_10_0_CLANG_X_2017-12-21-2300/src/SimG4Core/PhysicsLists/src/UrbanMscModel93.cc:(.text+0x2957): undefined reference to `G4MTHepRandom::getTheEngine()'
tmp/slc6_amd64_gcc630/src/SimG4Core/PhysicsLists/src/SimG4CorePhysicsLists/UrbanMscModel93.o: In function `UrbanMscModel93::SampleScattering(CLHEP::Hep3Vector const&, double)':
/build/mrodozov/CMSSW_10_0_CLANG_X_2017-12-21-2300/src/SimG4Core/PhysicsLists/src/UrbanMscModel93.cc:(.text+0x3512): undefined reference to `G4MTHepRandom::getTheEngine()'
/build/mrodozov/CMSSW_10_0_CLANG_X_2017-12-21-2300/src/SimG4Core/PhysicsLists/src/UrbanMscModel93.cc:(.text+0x3606): undefined reference to `G4MTHepRandom::getTheEngine()'
tmp/slc6_amd64_gcc630/src/SimG4Core/PhysicsLists/src/SimG4CorePhysicsLists/UrbanMscModel93.o:/build/mrodozov/CMSSW_10_0_CLANG_X_2017-12-21-2300/src/SimG4Core/PhysicsLists/src/UrbanMscModel93.cc:(.text+0x362c): more undefined references to `G4MTHepRandom::getTheEngine()' follow
clang-5.0: error: linker command failed with exit code 1 (use -v to see invocation)
config/SCRAM/GMake/Makefile.rules:2068: recipe for target 'tmp/slc6_amd64_gcc630/src/SimG4Core/PhysicsLists/src/SimG4CorePhysicsLists/libSimG4CorePhysicsLists.so' failed

Not sure if it comes from here but it's the most likely