Add atomic to mutable counters of MuonCaloTagTool

http://goetz.web.cern.ch/goetz/mutable_2019-06-10.html#Calo_Other

 nightly/master/2019-06-10T2153:Reconstruction/MuonIdentification/MuonCombinedBaseTools/src/MuonCaloTagTool.h +78


    76	    
    77	    // --- Internal cache ---
    78	    mutable int m_nTrueMuons;          //!< Counts the number true muons
    79	    mutable int m_nTracksTagged;       //!< Counts the number of tracks tagged
    80	    mutable int m_nMuonsTagged;        //!< Counts the number of truth muons tagged

nightly/master/2019-06-10T2153:Reconstruction/MuonIdentification/MuonCombinedBaseTools/src/MuonCaloTagTool.h +79


    77	    // --- Internal cache ---
    78	    mutable int m_nTrueMuons;          //!< Counts the number true muons
    79	    mutable int m_nTracksTagged;       //!< Counts the number of tracks tagged
    80	    mutable int m_nMuonsTagged;        //!< Counts the number of truth muons tagged
    81	    

nightly/master/2019-06-10T2153:Reconstruction/MuonIdentification/MuonCombinedBaseTools/src/MuonCaloTagTool.h +80


    78	    mutable int m_nTrueMuons;          //!< Counts the number true muons
    79	    mutable int m_nTracksTagged;       //!< Counts the number of tracks tagged
    80	    mutable int m_nMuonsTagged;        //!< Counts the number of truth muons tagged
    81	    
    82	    // --- Set up what to do and what not to do ---

Reconstruction/MuonIdentification/MuonCombinedBaseTools/src/MuonCaloTagTool.h

 /*
-  Copyright (C) 2002-2018 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2019 CERN for the benefit of the ATLAS collaboration
 */
 
 #ifndef MUONCOMBINEDBASETOOLS_MUONCALOTAGTOOL_H
@@ -32,6 +32,7 @@
 #include "StoreGate/ReadHandleKey.h"
 
 // - STL
+#include <atomic>
 #include <vector>
 
 
@@ -75,9 +76,9 @@ namespace MuonCombined {
     SG::ReadHandleKey<CaloCellContainer> m_caloCellCont{this,"CaloCells","AllCalo","calo cell container"};
     
     // --- Internal cache ---
-    mutable int m_nTrueMuons;          //!< Counts the number true muons
-    mutable int m_nTracksTagged;       //!< Counts the number of tracks tagged
-    mutable int m_nMuonsTagged;        //!< Counts the number of truth muons tagged
+    mutable std::atomic_int m_nTrueMuons;          //!< Counts the number true muons
+    mutable std::atomic_int m_nTracksTagged;       //!< Counts the number of tracks tagged
+    mutable std::atomic_int m_nMuonsTagged;        //!< Counts the number of truth muons tagged
     
     // --- Set up what to do and what not to do ---
     bool m_doCaloMuonTag;               //!< run CaloMuonTag Tool