This will add three gc fuzzing flags with 5% likelihood each to the second
correctness fuzzing config. The random checks are determined by the
top-level random-seed passed to the script.

This change depends on setting the fuzzer random seed as default to the
standard random seed, since the former isn't explicitly passed by
clusterfuzz.

NOTRY=true
TBR=hpayer@chromium.org

Bug: v8:7012
Change-Id: I794dc48bb953b6a95bbc4fc4305ad561bc13b6ee
Reviewed-on: https://chromium-review.googlesource.com/865912Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50577}