Fixed some warnings when using -Weffc++ gcc option

Plus some other icc warnings popped up with new and strictier
compile options.

No functional and speed change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/tt.h

@@ -102,6 +102,9 @@ struct TTCluster {
 
 class TranspositionTable {
 
+  TranspositionTable(const TranspositionTable&);
+  TranspositionTable& operator=(const TranspositionTable&);
+
 public:
   TranspositionTable();
   ~TranspositionTable();