[llvm] [DirectX] Fix `--dx-embed-debug` flag dependency (PR #210513)

[Jessica Clarke via llvm-commits]

https://github.com/jrtc27 approved this pull request.

Thanks for the quick fix; I can confirm this now builds with BUILD_SHARED_LIBS, and I see now that SourceInDebugModule already follows this approach (I should perhaps have delved slightly deeper before leaving my original comment on the other PR...).

https://github.com/llvm/llvm-project/pull/210513