[llvm] [KnownBitsTest] Common up isCorrect and isOptimal. NFC. (PR #89585)

[Paul Kirth via llvm-commits]

ilovepi wrote:

we're getting an assertion failure with this patch. I bisected it to this patch. I'm including a reproducer (not reduced) and my bisect script.

[repro.zip](https://github.com/llvm/llvm-project/files/15098610/repro.zip)


I bisected with 
```
git bisect good a2692ac23f1421097f0d51c7325045ed38db6408b
git bisect bad d3f6a88a1fb36f94c71940514e576821c6cc3ade
git bisect run bisect.sh
```
Note if you want to use the bisect script you may need to update paths. The `.cpp` and other `.sh` are from the generated reproducer, so should work if you update the path to clang in the script.

I have creduce running now, so I can probably post a smaller reproducer in a while.

In the meantime, can you revert this until a fix is ready?

https://github.com/llvm/llvm-project/pull/89585