TMVAImpFactory-Bs2MuMuDev1.cpp takes >10 min to compile
The file https://gitlab.cern.ch/lhcb/Rec/blob/beb3f6acdc429114ab5261687501bd59d341a08f/Rec/ChargedProtoANNPID/src/TMVAImpFactory-Bs2MuMuDev1.cpp takes excessively long to compile, which bottlenecks the build of Rec in highly parallel builds (see image). We should fix that.