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

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

I'm not in favor of this revert at the moment, but I'd like to hear more from our ABI folks (@rjmccall @hjl-tools specifically). It does not seem reasonable to me that we basically have no path forward to support `_BitInt` with larger sizes, which is one of the key points to the feature in the first place. Should Clang change the IR we produce for LLVM? Should LLVM change? Should the ABI change? Some combination of these?

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