second attempt to save pion root file

benchmarks/barrel_ecal/scripts/emcal_barrel_pions_analysis.cxx

@@ -20,6 +20,7 @@
 #include "TF1.h"
 #include "TH1D.h"
 #include <TFitResult.h>
+#include "TSystem.h"
 
 using ROOT::RDataFrame;
 using namespace ROOT::VecOps;