Add Boost::chrono to link libraries
The whole package makes extensive use of Boost::chrono but never links against it. That worked with the old FindBoost.cmake which adds implicit dependencies on its own. With the switch to Bootst own CMake config files this is no longer the case.
This problem is not seen at compile time only when HLTMPPU_main is run
LD_BIND_NOW=1 HLTMPPU_main