[llvm] [CI] Enable CIR testing for all MLIR and Clang changes (PR #227834)

[Aaron Ballman via llvm-commits]

AaronBallman wrote:

> @AaronBallman Do you have any objections to enabling CIR CI testing for all Clang changes?

On it's face? No. But if enabling that testing means precommit CI takes so much longer to complete that it causes a significant backlog of precommit CI work at high-volume times, that might be problematic enough to require holding off. I'm particularly worried in the short-term because squash and merge is broken and so the current advice is to update branch and enable auto-merge, which means a lot of PRs are getting additional (but unnecessary) rounds of CI runs. So my answer is qualified by "assuming the infrastructure people are not concerned".

https://github.com/llvm/llvm-project/pull/227834