This patch is to avoid spilling the phi at the loop header if there is a back-edge with an input for the phi that interferes with the phi's value, because in case that input gets spilled it might introduce a stack-to-stack move at the back-edge.

Bug: chromium:1063831
Change-Id: Ie7129f10fb573cc799c588e6639b5ad486ea520d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2152002
Commit-Queue: Yolanda Chen <yolanda.chen@intel.com>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67299}