This removes a bunch of porting helpers, e.g. scopes that mark
the addressability of ebx, printing embedded builtin candidates, and
the call/jump mechanism through a virtual target register.

This also disables root register verification by default on ia32. It
can be completely removed in a bit.

Bug: v8:6666
Change-Id: I4705d61991ddc57c30981c311a1c8c5e2f8ddf4d
Reviewed-on: https://chromium-review.googlesource.com/c/1288271Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56864}