The build script currently is doing some unnecessary steps:
- Running `gclient` only prints out an help message. It is a step
indicated in various documentations, but is only necessary to keep
depot-tools up-to-date, which they are, since we just cloned it.
- The `fetch v8` command creates a v8 directory, no need to create
another layer.
- `gclient sync` is run as part of `fetch`. Same as `gclient`, this step
is only given in documentations to keep things up-to-date on an existing
clone, but we just freshly got one.
- Same goes for `git pull && gclient sync`
- `git checkout master` is not necessary, as `fetch` gets us there
already (albeit, in a detached head state)
- install-build-deps.sh installs build dependencies for chrome or
whatever. That's way too much for v8, that barely needs pkg-config and
glib, which we now install in the docker image.
Differential Revision: https://phabricator.services.mozilla.com/D20082
901d68ed91