This is part of JSSP removal for arm64. The padding is needed so
that the extra arguments, which are pushed separately from the rest
of the arguments, will take up an even number of slots, to avoid
copying the rest of the arguments one slot down.

Bug: v8:6644
Change-Id: I00a8730c375e4b4cc8fa0c8b6372751f92754466
Reviewed-on: https://chromium-review.googlesource.com/713255
Commit-Queue: Georgia Kouveli <georgia.kouveli@arm.com>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48547}