[clang] [Clang] Consider preferred_type in bitfield warnings (#116760) (PR #116785)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

@erichkeane @Fznamznon what should the release note be - just something akin to "added warning flag -W... to warn when bitfield packing differs from MSVC"?

https://github.com/llvm/llvm-project/pull/116785