Fix use of CLHEP to be compatible with Gaudi new cmake configuration
When using Gaudi with new CMake configuration CLHEP has to be used in a slightly different way.
This was breaking compilation with DD4hep. The problem has not been completely understood but is due to a mix of 2 ways of finding CLHEP in cmake : findCLHEP.cmake and CLHEPCondig.cmake. We now ensure that only CLHEPCondig.cmake is used.
Edited by Rosen Matev