[llvm] [Object,ELF] Implement PN_XNUM extension for program headers (PR #165284)

[James Henderson via llvm-commits]

https://github.com/jh7370 approved this pull request.

For the record, if something like this happens again and your original PR has been approved, you don't need to (currently) wait for re-approval of a new, identical PR.

Please however add a link to the original PR in your description, for traceability purposes.

https://github.com/llvm/llvm-project/pull/165284