C++ introduces the {alignas} keyword, which can be used with types or
integral constant expressions. Use this instead of the V8_ALIGNAS (for
types) or V8_ALIGNED (for integral constants) macros.

R=ulan@chromium.org

Bug: v8:8562
Change-Id: I54999b56a5715237f88c63d8543ef728a5b2eff5
Reviewed-on: https://chromium-review.googlesource.com/c/1379935Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58290}