[clang] [HLSL] Don't invoke `dxv` from `clang-dxc` for text output (PR #135876)

[Deric C. via cfe-commits]

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

This is great! Now I don't have to specify `-Vd` when I run clang-dxc without `-Fo` :)

https://github.com/llvm/llvm-project/pull/135876