[llvm] [DAG] Always allow folding XOR patterns to ABS pre-legalization (PR #94601)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

@davemgreen I've had to pull out a few ARM-specific changes from #94504 to prevent infinite loops re-expanding vXi64 ABS.

We've lost the neon vabdl.u32 pattern, do you want me to tweak the neon tablegen pattern in this patch? It will be removed entirely in #94504 which should be ready to go immediately after this patch.

https://github.com/llvm/llvm-project/pull/94601