GCC doesn't have __attribute__((require_constant_initialization)). Use
it only for clang.

Bug: chromium:1325007
Change-Id: Ide5d428ed107d3244072774c0031c042ed0cee31
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3735125Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81447}