[llvm] X86: Emit adox instead of adc for overflow add (PR #216609)

[via llvm-commits]

zero318 wrote:

> The description of what case this applies to could be improved.

The intended use case is to provide additional folds for the new OF patterns in #216581, #216590, and #216607. Unsigned logic can already emit `ADC` instead of separate `SETC`/`ADD`, so this extends that to `ADOX` instead of `SETO`/`ADD`.

https://github.com/llvm/llvm-project/pull/216609