[llvm] [DirectX][ObjectYAML] Attempt to fix flaky PRIVPart.yaml (PR #206278)

[Dmitry Vasilyev via llvm-commits]

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

I think the issue was with `2>&1` so stdin and stdout were getting mixed up.
Anyway I prefer a separate temporary binary file do be sure.
LGTM

https://github.com/llvm/llvm-project/pull/206278