[TDF] Avoid unused variable warnings

Author: eguiraud

tree/treeplayer/inc/ROOT/TDFInterface.hxx

@@ -1305,6 +1305,7 @@ private:
          // hack to expand a template parameter pack without c++17 fold expressions.
          std::initializer_list<int> expander{
             (mustBeDefined[S] ? DefineDSColumnHelper<ColumnTypes>(columns[S], lm) : /*no-op*/((void)0), 0)...};
+         (void)expander; // avoid unused variable warnings
       }
    }
 

tree/treeplayer/inc/ROOT/TDataSource.hxx

@@ -46,7 +46,7 @@ public:
    /// Convenience method called at the start of each task, before processing a range of entries.
    /// DataSources can implement it if needed (does nothing by default).
    /// firstEntry is the first entry of the range that the task will process.
-   virtual void InitSlot(unsigned int slot, ULong64_t firstEntry) {}
+   virtual void InitSlot(unsigned int /*slot*/, ULong64_t /*firstEntry*/) {}
 
 protected:
    /// type-erased vector of pointers to pointers to column values - one per slot