[llvm] [AArch64][GlobalISel] Take abs scalar codegen closer to SDAG (PR #84886)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

Even if SMAX and lowerAbsToAddXor are legal, shouldn't we have the means to say for FOO cores, we prefer SMAX, and for BAR cores we prefer Xor?

https://github.com/llvm/llvm-project/pull/84886