Clang fixes for TrigServices
Fix warnings + errors in TrigServices clang build (see http://atlas-computing.web.cern.ch/atlas-computing/links/distDirectory/gitwww/GITWebArea/nightlies/master/2019-11-03T2110/Athena/x86_64-centos7-clang8-opt/Athena/HLT.Trigger.TrigControl.TrigServices.log.html)
Hopefully nothing controversial.