[clang] Revert "[X86][clang] Lift _BitInt() supported max width." (PR #81175)

[Nikita Popov via cfe-commits]

nikic wrote:

Thanks for providing proper context. The second issue does look pretty serious to me. It's a regression from the i128 alignment changes in LLVM 18.

It should be technically possible for Clang to give `_BitInt(N)` an alignment that is independent from LLVM's alignment, but clearly Clang doesn't do everything that's necessary for that now, such as emitting GEPs in canonical i8 form with explicitly LLVM-independent offset calculation.

https://github.com/llvm/llvm-project/pull/81175