[llvm] [CI] Update Windows premerge testing to use clang-cl.exe (PR #164900)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

You'll need to relaunch this job to get testing once https://github.com/llvm/llvm-project/actions/runs/18761757077/job/53527832407 finishes uploading the new image.

https://github.com/llvm/llvm-project/pull/164900