In gcc8, std::pair derives from the (empty) base class std::__pair_base.
When ROOT makes dictionaries, it likes to strip std:: qualifiers.
When it then tries to look up cling information for a TClass,
if the lookup fails, it tries again with the std:: reinserted
for all STL classes (with TClassEdit::InsertStd()).
However, that doesn't work for __pair_base, because it's not a class
that ROOT knows about.  The upshot is that we see errors like:

  Error in <TClass::LoadClassInfo>: no interpreter information for class __pair_base<unsigned int,string> is available even though it has a TClass initialization routine.

We work around this by hooking into ROOT's TClass creation.
If we see a std::pair class, we erase the base class information
from its TClass.

Create pile-up events hash and store it in xAOD::EventInfo, master edition (ATLASSIM-3795)

See merge request atlas/athena!21398

SECOND TRY: Add support for complex jet chains. Temporarily limit menu items for simple chains.

See merge request atlas/athena!21759

AtlasPyFwdBwdPorts: remove enum34 module

See merge request atlas/athena!22075

Drop keyless retrieve of xAOD::EventInfo in CscDigitizationTool

See merge request atlas/athena!22091

Dealing with Multiple McEventCollections

See merge request atlas/athena!21993

Manual sweep of athenaprivate1!16317 from 21.0 to master: workaround for the issues seen when passing zero lifetime particles to Geant4 (ATLASSIM-3313)

See merge request atlas/athena!22026

Fixed an issue that L2MuonSA can't work in the newJO test due to wrong values of MDT circles, ATR-16944

See merge request atlas/athena!22042

TileMonitoring: Migrate monitoring Tile time with jets for Run 3

See merge request atlas/athena!22057

GeoPrimitives: Drop backwards compatibility with Eigen <= 3.3.0

See merge request atlas/athena!22073

G4DebuggingTools: declare public headers

See merge request atlas/athena!22076

TrigEgammaEmulationTool: Fix variable naming

See merge request atlas/athena!22080

Moving code for electron chain setup from TUT to TMMT

See merge request atlas/athena!21596

R-hadron cleanup for master

See merge request atlas/athena!22034

Add HLT timeout handling and improve handling of other errors

See merge request atlas/athena!21931

disable access to the offline conditions in the online mode - it fixes  ATLASRECTS-4865

Closes ATLASRECTS-4865

See merge request atlas/athena!21874

Consider bad SCT strips in InDetTrackHoleSearchTool (ATLASRECTS-4902)

See merge request atlas/athena!22070

LongLivedParticleDPDMaker: Remove reference to xAOD::EventInfo.

See merge request atlas/athena!22062

CaloCondPhysAlgs: Use conditions handle to read hvcorr information.

See merge request atlas/athena!22069

TrigT1CaloToolInterfaces+TrigT1CaloTools: Make most methods of IL1CPMTools const.

See merge request atlas/athena!22061

CscDigitizationTool was retrieving an `xAOD::EventInfo` object from the
`evtStore` and storing the event and run numbers in member variables.
These values were only used in two DEBUG messages.

Change variable names to comply with ATLAS naming convention and to
avoid compilation warnings.

Add the PUBLIC_HEADERS in the cmake configuration to properly install
them (and to avoid the cmake warning).

SCT_RawDataByteStreamCnv: Updating SCT_RodDecoder according to ATLAS Coding Guidelines

See merge request atlas/athena!22009

TrigMessageSvc: modernize and sync with Gaudi/master

See merge request atlas/athena!22012

Manual sweep of !21768 from '21.0' to 'master: Protection for empty GenEvents in BeamEffectsAlg::patchSignalProcessVertex(...)

See merge request atlas/athena!22015

LArMonTools: Use conditions handle to read hvcorr information.

See merge request atlas/athena!22058

DecisionHandling: remove pure virtual overrides from Hypo/InputMakerBase

See merge request atlas/athena!22023

athenaHLT: add option to debug fork and fix timeout

See merge request atlas/athena!22021

enum34 is provided by LCG_95 now.

Drop the support of older Eigen versions and cleanup dictionary rules.

TrigT1Interfaces: Fix gcc9 warnings.

See merge request atlas/athena!22059