[clang] [clang-tools-extra] [flang] [lldb] [llvm] [openmp] [pstl] Finally formalise our defacto line-ending policy (PR #86318)

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

> > if all tests would have been cleaned up before this
> 
> That was most certainly my intention, and I saw green before merging, so I must've looked in the wrong place

Ah, right - as we've seen that the CI runner normally only updates an existing checkout, where changes to gitattributes like these don't really take effect, I guess this can be understood.

(Plus there are a number of tests in less frequently executed testsuites, like compiler-rt, clang-tools-extra, and in `llvm/utils/lit/tests`, that don't necessarily get included in each normal run in CI.)

On that topic - some of the scripts that orchestrate that premerge testing lives in `.ci/generate-buildkite-pipeline-premerge`. By editing that script, it should be possible to trigger it to run all possible testsuites, not just the ones currently touched. And I'm wondering if there's anything we could add there temporarily (both right now, to flush the current checkouts on the premerge cluster, and when testing PRs like this one), to force it to check files out again?

https://github.com/llvm/llvm-project/pull/86318