Two folds are happening here:

- https://rise4fun.com/Alive/oaFX
- And then
`foldICmpWithHighBitMask()`(D52001): https://rise4fun.com/Alive/wsP4

This change doesn't just add the handling for eq/ne predicates,

it actually builds upon the previous `foldICmpWithLowBitMaskedVal()` work,

so **all** the 16 fold variants* are immediately supported.

I'm indeed only testing these two predicates.

I do not feel like re-proving all 16 folds*, because they were already proven

for the general case of constant with all-ones in low bits. So as long as

the mask produces all-ones in low bits, i'm pretty sure the fold is valid.

But required, i can re-prove, let me know.

- eq/ne are commutative - 4 folds; ult/ule/ugt/uge - are not commutative (the commuted variant is InstSimplified), 4 folds; slt/sle/sgt/sge are not commutative - 4 folds. 12 folds in total.

https://bugs.llvm.org/show_bug.cgi?id=38123

https://bugs.llvm.org/show_bug.cgi?id=38708