CxxUtils: Make exctrace properly MT-safe.

Update the exctrace collector to work properly in a MT environment. Change the static variables holding the trace to be thread_local. Further, retrieve the saved trace via calling a function, rather than accessing the variables directly.

This merge request affects 1 package:

• Control/CxxUtils

This merge request affects 5 files:

• Control/CxxUtils/CxxUtils/SealDebug.h
• Control/CxxUtils/CxxUtils/exctrace.h
• Control/CxxUtils/Root/SealDebug.cxx
• Control/CxxUtils/Root/exctrace.cxx
• Control/CxxUtils/src/exctrace/exctrace_collector.cxx

Adding @ssnyder ,@rbianchi as watchers

added Core master review-pending-level-1 labels

CI Result SUCCESS (hash 658bf04d)

	Athena	AthSimulation	AthGeneration	AnalysisBase	AthAnalysis	DetCommon
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
AthAnalysis: number of compilation errors 0, warnings 0
DetCommon: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 30782]

Hi,
I'm passing this to a Level-2 shifter since they can have a much better understanding on thread-safety.

Cheers,
Francisco (L1)

added review-pending-level-2 label and removed review-pending-level-1 label

MR looks good. Approving.

Cheers, Abhishek [L2]

added review-approved label and removed review-pending-level-2 label

merged

mentioned in commit db1d39e8

added sweep:ignore label