[RF] Avoid deprecation warning when building RooFit

When RooFit builds itself, it should be possible to use deprecated
functions in other deprecated functions without causing a warning at
build time.

roofit/roofitcore/inc/RooDataSet.h

@@ -45,7 +45,10 @@ class RooDataSet : public RooAbsData, public RooDirItem {
     // Constructor for subset of existing dataset
   RooDataSet(RooStringView name, RooStringView title, RooDataSet *data, const RooArgSet& vars,
              const char *cuts=nullptr, const char* wgtVarName=nullptr)
-  R__DEPRECATED(6,38, "Use RooAbsData::reduce(), or if you need to change the weight column, the universal constructor with the Import(), Cut(), and WeightVar() arguments.");
+#ifndef ROOFIT_BUILDS_ITSELF
+  R__DEPRECATED(6,38, "Use RooAbsData::reduce(), or if you need to change the weight column, the universal constructor with the Import(), Cut(), and WeightVar() arguments.")
+#endif
+  ;
   RooDataSet(RooStringView name, RooStringView title, RooDataSet *data, const RooArgSet& vars,
              const RooFormulaVar& cutVar, const char* wgtVarName=nullptr)
   R__DEPRECATED(6,38, "Use RooAbsData::reduce(), or if you need to change the weight column, the universal constructor with the Import(), Cut(), and WeightVar() arguments.");