[ELF] Keep non-alloc orphan sections at the end

https://reviews.llvm.org/D85867 changed the way we assign file offsets
(alloc sections first, then non-alloc sections).

It also removed a non-alloc special case from `findOrphanPos`.
Looking at the memory-nonalloc-no-warn.test change, which would be
needed by #93761, it makes sense to restore the previous behavior: when
placing non-alloc orphan sections, keep these sections at the end so
that the section index order matches the file offset order.

This change is cosmetic. In sections-nonalloc.s, GNU ld places the
orphan `other3` in the middle and the orphan .symtab/.shstrtab/.strtab
at the end.

Pull Request: https://github.com/llvm/llvm-project/pull/94519