Don't own the buffer in object::Binary.

Owning the buffer is somewhat inflexible. Some Binaries have sub Binaries
(like Archive) and we had to create dummy buffers just to handle that. It is
also a bad fit for IRObjectFile where the Module wants to own the buffer too.

Keeping this ownership would make supporting IR inside native objects
particularly painful.

This patch focuses in lib/Object. If something elsewhere used to own an Binary,
now it also owns a MemoryBuffer.

This patch introduces a few new types.

* MemoryBufferRef. This is just a pair of StringRefs for the data and name.
  This is to MemoryBuffer as StringRef is to std::string.
* OwningBinary. A combination of Binary and a MemoryBuffer. This is needed
  for convenience functions that take a filename and return both the
  buffer and the Binary using that buffer.

The C api now uses OwningBinary to avoid any change in semantics. I will start
a new thread to see if we want to change it and how.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216002 91177308-0d34-0410-b5e6-96231b3b80d8

tools/obj2yaml/obj2yaml.cpp

@@ -32,11 +32,11 @@ static std::error_code dumpInput(StringRef File) {
   if (File != "-" && !sys::fs::exists(File))
     return obj2yaml_error::file_not_found;
 
-  ErrorOr<std::unique_ptr<Binary>> BinaryOrErr = createBinary(File);
+  ErrorOr<OwningBinary<Binary>> BinaryOrErr = createBinary(File);
   if (std::error_code EC = BinaryOrErr.getError())
     return EC;
 
-  Binary &Binary = *BinaryOrErr.get();
+  Binary &Binary = *BinaryOrErr.get().getBinary();
   // TODO: If this is an archive, then burst it and dump each entry
   if (ObjectFile *Obj = dyn_cast<ObjectFile>(&Binary))
     return dumpObject(*Obj);