Revert r194865 and r194874.

This change is incorrect. If you delete virtual destructor of both a base class
and a subclass, then the following code:
  Base *foo = new Child();
  delete foo;
will not cause the destructor for members of Child class. As a result, I observe
plently of memory leaks. Notable examples I investigated are:
ObjectBuffer and ObjectBufferStream, AttributeImpl and StringSAttributeImpl.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194997 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ExecutionEngine/ObjectBuffer.h

@@ -33,6 +33,7 @@ class ObjectBuffer {
 public:
   ObjectBuffer() {}
   ObjectBuffer(MemoryBuffer* Buf) : Buffer(Buf) {}
+  virtual ~ObjectBuffer() {}
 
   /// getMemBuffer - Like MemoryBuffer::getMemBuffer() this function
   /// returns a pointer to an object that is owned by the caller. However,
@@ -57,6 +58,7 @@ protected:
 class ObjectBufferStream : public ObjectBuffer {
 public:
   ObjectBufferStream() : OS(SV) {}
+  virtual ~ObjectBufferStream() {}
 
   raw_ostream &getOStream() { return OS; }
   void flush()