Fix a gcc warning:

'class llvm::DAGDeltaAlgorithm' has virtual functions and accessible non-virtual destructor

Not sure if this is the best solution, but this class has state and some of the
classes that inherit from it also do, so it looks appropriate.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@105675 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/DAGDeltaAlgorithm.h

@@ -45,6 +45,8 @@ public:
   typedef std::vector<changeset_ty> changesetlist_ty;
 
 public:
+  virtual ~DAGDeltaAlgorithm() {}
+
   /// Run - Minimize the DAG formed by the \arg Changes vertices and the \arg
   /// Dependencies edges by executing \see ExecuteOneTest() on subsets of
   /// changes and returning the smallest set which still satisfies the test