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/Bitcode/ReaderWriter.h

@@ -30,8 +30,7 @@ namespace llvm {
   /// deserialization of function bodies.  If successful, this takes ownership
   /// of 'buffer. On error, this *does not* take ownership of Buffer.
   ErrorOr<Module *> getLazyBitcodeModule(MemoryBuffer *Buffer,
-                                         LLVMContext &Context,
-                                         bool BufferOwned = true);
+                                         LLVMContext &Context);
 
   /// getStreamedBitcodeModule - Read the header of the specified stream
   /// and prepare for lazy deserialization and streaming of function bodies.