[TargetLowering][ARM][AArch64] Remove usage of NoSignedWrap/NoUnsignedWrap from AVGFLOOR/CEIL transform.

[craig.topper]

Summary

Use computeOverflowForUnsignedAdd and computeOverflowForSignedAdd
instead. Unfortunately, this recomputes some known bits and sign bits
we may have already computed, but was the easiest fix without a lot
of restructuring.

This recovers the regressions from D151472.

[RKSimon]

LGTM with one possible minor

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

1050

I added DAG::computeOverflowForAdd wrapper to allow us to merge Signed/Unsigned paths - not sure if its useful here?

[craig.topper]

Use Simon's suggestion.