[llvm] [SelectionDAG] Preserver poison for abs INT_MIN lowering (PR #183851)

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aryanmagoon wrote:

@RKSimon Added ISD::ABS_MIN_POISON to preserve llvm.abs(x, true). This would now let compiler skip freeze instructions during expansion. Other targets opt in by simply setting ISD::ABS_MIN_POISON as legal and adding a TableGen pattern in the target's .td file as shown with NVPTX. 

https://github.com/llvm/llvm-project/pull/183851