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

[Dmitry Vasilyev via llvm-commits]

slydiman wrote:

I think it is a bad idea to transfer raw binary data via stdin on Windows. On Windows, standard streams (stdin, stdout, stderr) open in the text mode by default, which corrupts raw binary data, halts reading if it encounters a 0x1A byte (the Ctrl+Z EOF marker), etc.

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