The instruction selector assumed for Word32AtomicPairBinop nodes that if
there exists a Projection(1) user, then there also exists a
Projection(0) user. This, however, is not the case, because TurboFan
eliminates unreachable nodes. The missing projection node lead to a
failed DCHECK in the register allocator.

With this CL we allocate the right registers for the existing
projections, and allocate the other needed registers as temp registers.

R=gdeepti@chromium.org

Bug: v8:10140
Change-Id: I22331cae58f933e89dac6993fe3b21ff6502838a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2011829Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65941}