Makes ClusterFuzz start fuzzing with the flag on.

BUG=v8:5516

Change-Id: Ia80f7d22f12fe25efb226102a896e8b0e3537947
Reviewed-on: https://chromium-review.googlesource.com/610000
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47366}