LArMonitoring: cmake fixes

Don't build an object into more than one library.

This merge request affects 3 files:

• LArCalorimeter/LArMonitoring/CMakeLists.txt
• LArCalorimeter/LArMonitoring/src/LArStrHelper.cxx
• LArCalorimeter/LArMonitoring/src/StrHelper/LArStrHelper.cxx

Adding @pavol as watcher

added DQ JetEtmiss LAr master review-pending-level-1 labels

CI Result SUCCESS (hash 1b6ab863)

	Athena	AthSimulation	AthGeneration	AnalysisBase
externals
cmake
make
required tests
optional tests

Full details available on this CI monitor view
Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
AthGeneration: number of compilation errors 0, warnings 0
AnalysisBase: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 23710]

added review-approved label and removed review-pending-level-1 label

merged

mentioned in commit 242cf115

added sweep:ignore label