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

[Harald van Dijk via cfe-commits]

hvdijk wrote:

> I would really like to avoid Clang 18 being released in this broken state, if possible, and I see no way short of a revert to realistically achieve that.

It's too late for that now, it's out there, and it's now everybody else's problem regardless of what Clang does in the future. Because of that, this PR no longer serves its purpose.

I cannot imagine that even a single user will be happy with this, but this is what you decided. So be it.

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