[llvm] [DirectX] Add GlobalDCE pass after finalize linkage pass in DirectX backend (PR #151071)

[Deric C. via llvm-commits]

Icohedron wrote:

> @Icohedron are you aware of any changes that went in that could have impacted these validation issues? Is it possible the bitcast errors are masking the unused errors?

No, I am not aware of any changes that could have impacted these validation issues. I also don't think the bitcast errors are masking the unused errors because they used to coexist.

https://github.com/llvm/llvm-project/pull/151071