This will download a prebuilt bazel on Ubuntu bots if gclient variable
download_prebuilt_bazel is set. The currently pinned version is:
5.0.0-pre.20210604.6.

This is planned to only run on specific bots that use a new recipe
for building with bazel:
https://crrev.com/c/2972749

Bug: v8:11912
Change-Id: I8ff405fc03bfede4762bf4e8577cb1feab56f7c4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2972918
Auto-Submit: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Liviu Rau <liviurau@chromium.org>
Reviewed-by: Liviu Rau <liviurau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75288}