[llvm] [DirectX] Convert private global variables to internal linkage during Finalize Linkage pass (PR #146406)

[Farzon Lotfi via llvm-commits]

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

I'm fine with this change. I beleive Justin's concerns can be addressed when we put up a pr for https://github.com/llvm/llvm-project/issues/139023

https://github.com/llvm/llvm-project/pull/146406