This CL ensures that ConstructBoundFunction and
ConstructedNonConstructable preserve the kRootRegister (ebx).

Bug: v8:6666
Change-Id: I5aaee07aee9377f62028c98ccc8c6fdfe23dbc6d
Reviewed-on: https://chromium-review.googlesource.com/1233615
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56033}