adding extern declaration (#7525)

Author: jgrosseo

Framework/Core/include/Framework/AnalysisDataModel.h

@@ -336,6 +336,7 @@ using TrackExtra = TracksExtra::iterator;
 } // namespace aod
 namespace soa
 {
+extern template struct soa::Join<aod::Tracks, aod::TracksExtra>;
 extern template struct soa::Join<aod::Tracks, aod::TracksCov, aod::TracksExtra>;
 extern template struct soa::Join<aod::TracksExtension, aod::StoredTracks>;
 } // namespace soa

Framework/Core/src/AnalysisDataModel.cxx

@@ -13,6 +13,7 @@
 namespace o2::soa
 {
 template struct Join<aod::BCs, aod::Timestamps>;
+template struct Join<aod::Tracks, aod::TracksExtra>;
 template struct Join<aod::Tracks, aod::TracksCov, aod::TracksExtra>;
 template struct Join<aod::FwdTracks, aod::FwdTracksCov>;
 template struct Join<aod::TransientV0s, aod::StoredV0s>;