[clang] [clang][layout] Fix unsigned char overflow in ms_struct bitfield layout (PR #181433)

[Fangrui Song via cfe-commits]

MaskRay wrote:

The merged commit has `Akram Hany <109467185+akramhany at users.noreply.github.com>` as the author. We discourage "hidden user" but the check did not take effect for this instance
https://discourse.llvm.org/t/hidden-emails-on-github-should-we-do-something-about-it/74223/84?u=maskray

https://github.com/llvm/llvm-project/pull/181433