This avoid introduction of {TypeGuard} nodes during load elimination.
Such type guard could lead to contradicting type information where a
constant {NumberConstant} node was guarded to have {ExternalPointer}
type, which would lead to an impossible constraint on representation
selection.

R=jarin@chromium.org
TEST=mjsunit/regress/regress-crbug-752826
BUG=chromium:752826

Change-Id: Ida3815af24ccc8a48474b8d66117b9718f61adda
Reviewed-on: https://chromium-review.googlesource.com/605547Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47218}