If memory is statically known to be out of bounds, do not generate code
for the load or store, and also mark the rest of the current block
unreachable to avoid unnecessary code generation.
This also prevents us from having to special-case illegal memory
offsets in the LiftoffAssembler. For valid code, the offset will always
be smaller than 2GB.

R=ahaas@chromium.org

Bug: v8:6600
Change-Id: Ib5a9006780098e9f2ab9eda4bac7939f15612ae0
Reviewed-on: https://chromium-review.googlesource.com/939821Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51623}