[llvm] [ARM] Replace ABS and tABS machine nodes with custom lowering (PR #156717)

[via llvm-commits]

AZero13 wrote:

> This sounds like a nice cleanup. I've wondered why the default lowering used these ABS pseudos. It is a shame it needs custom lowers, that can have downsides, but in this case with the custom lowering being so odd and the midend already canonicalizing to abs instructions it probably makes sense.
> 
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> Can you update the costs to match the expansion?

Already done did you see? 

https://github.com/llvm/llvm-project/pull/156717