[clang] [clang-cl][flang][dxc] Fix opts exposed to clang-cl/dxc by mistake (PR #118640)

[Mészáros Gergely via cfe-commits]

Maetveis wrote:

> Can we keep this flag for CL in this PR and open an issue to discuss whether it should be disabled for CL?

Sure, see latest commit and https://github.com/llvm/llvm-project/issues/119179.

https://github.com/llvm/llvm-project/pull/118640