[clang] [clang][NFC] Annotate `Type` bit-fields with `clang::preferred_type` (PR #70349)

[Timm Baeder via cfe-commits]

tbaederr wrote:

Since this is done unconditionally, doesn't this mean we now need an unreleased clang to compile? Or are `[[clang::]]` attributes just ignored if they are unknown?

https://github.com/llvm/llvm-project/pull/70349