This especially simplifies arm64 CallApiCallbackStub alignemnt handling.

Bug: 
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I26e9c075702161a3f1c70f94ec83d149d2d8f33a
Reviewed-on: https://chromium-review.googlesource.com/741600Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49004}