[llvm] [X86] abs i8 - perform as abs i32 if we have access to CMOV (PR #95101)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

It's annoying that we end up having to copy/extend the non-negated param:
```asm
movsbl %dil, %ecx
movl %ecx, %eax
negl %eax
cmovsl %ecx, %eax
```
when we should be able to get away with
```asm
movsbl %dil, %eax
negl %eax
cmovnsl %edi, %eax
```

https://github.com/llvm/llvm-project/pull/95101