[Layout] Assign ordinals in Resolution order.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@192277 91177308-0d34-0410-b5e6-96231b3b80d8
[cleanup] remove unused private variable

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@192278 91177308-0d34-0410-b5e6-96231b3b80d8