The code target vector is used by backends whenever initial code
creation uses immediates that cannot hold a code pointer: An index into
the vector is used instead, and the vector contains the corresponding
code object. This CL makes the code target vector available on all
platforms.

Bug: v8:6666
Change-Id: I2026acd6a77a3465fe2285b84d47866c3b794855
Reviewed-on: https://chromium-review.googlesource.com/1118885
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54236}