[clang] [Clang] Fix offsetof sign-extending unsigned array indices >= 128 (PR #204139)

[Marlus Cadanus da Costa via cfe-commits]

marlus wrote:

There's a conflict in clang/docs/ReleaseNotes.rst should I resolve it, or will you handle it during the merge?

https://github.com/llvm/llvm-project/pull/204139