Make ObjectFile and BitcodeReader always own the MemoryBuffer.

This allows us to just use a std::unique_ptr to store the pointer to the buffer.
The flip side is that they have to support releasing the buffer back to the
caller.

Overall this looks like a more efficient and less brittle api.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211542 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/Module.h

@@ -458,7 +458,7 @@ public:
   /// Make sure all GlobalValues in this Module are fully read and clear the
   /// Materializer. If the module is corrupt, this DOES NOT clear the old
   /// Materializer.
-  std::error_code materializeAllPermanently();
+  std::error_code materializeAllPermanently(bool ReleaseBuffer = false);
 
 /// @}
 /// @name Direct access to the globals list, functions list, and symbol table