[clang] [clang-tools-extra] [lldb] [clang] Remove intrusive reference count from `DiagnosticOptions` (PR #139584)

[via cfe-commits]

https://github.com/cor3ntin approved this pull request.

The clang parts look like a nice improvement, thanks!

Please wait for a few other people to review it though.

https://github.com/llvm/llvm-project/pull/139584