The "stress_background_compile" variant runs on all our bots. We
combine it with testing wasm code GC (which kind of fits into
background compile stressing) to get more coverage for that. Both
features are orthogonal, so we can test both at the same time without
loosing any coverage.

R=machenbach@chromium.org
CC=rmcilroy@chromium.org

Bug: v8:8217
Change-Id: Ib17decd4869978ff98e302694fa73d70ceec120e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1588472Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61151}