The ctors dispatch between atomic and non-atomic writes; there's no
need for a default initializer.

Bug: chromium:1292728
Change-Id: I2b4c3341ee2d2682ba0113c8366456147ebc717e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3429201Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78884}