add a destructor to silence the compiler warnings

dtool/src/dtoolbase/memoryHook.cxx

@@ -140,6 +140,17 @@ MemoryHook(const MemoryHook &copy) :
 #endif
 }
 
+////////////////////////////////////////////////////////////////////
+//     Function: MemoryHook::Destructor
+//       Access: Public, Virtual
+//  Description: 
+////////////////////////////////////////////////////////////////////
+MemoryHook::
+~MemoryHook() {
+  // Really, we only have this destructor to shut up gcc about the
+  // virtual functions warning.
+}
+
 ////////////////////////////////////////////////////////////////////
 //     Function: MemoryHook::heap_alloc
 //       Access: Public, Virtual

dtool/src/dtoolbase/memoryHook.h

@@ -33,6 +33,7 @@ class EXPCL_DTOOL MemoryHook {
 public:
   MemoryHook();
   MemoryHook(const MemoryHook &copy);
+  virtual ~MemoryHook();
 
   virtual void *heap_alloc(size_t size);
   virtual void heap_free(void *ptr);