Unreachable code may consume values from an empty stack as needed, known
as stack polymorphism. After consuming the values, the stack height
should still be 0, which was incorrectly handled by multi-value blocks.

R=ahaas@chromium.org

Bug: chromium:1085507
Change-Id: Ibf5f2d05bec0fbe029cfa66ee2d07540a370934a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2218033Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68070}