Re-unique_ptrify LoadedObjectInfo::clone after it was reverted due to some...

Re-unique_ptrify LoadedObjectInfo::clone after it was reverted due to some other changes that broke on GCC around the same time

Apparently this functionality isn't used in-tree (or I would go & make
the explicit unique_ptr constructions into implicit constructions to
make them more self documenting now that clone doesn't return a raw
owning pointer anymore) but only by the Julia frontend. This isn't
ideal.

llvm-svn: 239091