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

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> I must have missed this PR originally. I oppose letting Git change any line endings. It always ends like this.

Also just for context - the Clang precommit CI is allegedly still broken, because those buildbots happened to be restarted when we had these gitattributes in place, so all files are checked out with CRLF right now, and any incremental update on top doesn't change that, as long as those files aren't touched: https://discourse.llvm.org/t/windows-premerge-buildbot-broken-for-5-days/82571/6

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