[llvm] [AArch64] Lower disjoint_or+not to eon. (PR #147279)

[Ricardo Jesus via llvm-commits]

rj-jesus wrote:

> question: does ORN not exist on AArch64? was curious as to why the non-disjoint ors don't fold to that

ORN does exit, but it doesn't implement `NOT (ORR (a, b))`; it implements `OR (a, NOT (b))`.
(Technically EON it's the same, but it just so happens that NOT (EOR (a, b)) = EOR (a, NOT (b)).)

https://github.com/llvm/llvm-project/pull/147279