[infra] Add shadow opt-in builder for V8 Linux64 - gcov coverage

Bug: v8:11594
Change-Id: I29dd481a22ee3c131807293664154865e7990098
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2810781


Commit-Queue: Almothana Athamneh <almuthanna@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73863}