In the docker build script that Kokoro runs, the directories
are owned by a different user. Git complains about that and in the GN
flow GN will error out.
In this docker flow we don't care about that warning, so within
the docker config set a git global option to ignore the issue.
Add missing `.cfg` files for GN presubmit.
Add missing `recursedeps` in the `DEPS` file.
Call `./update_glslang_sources.py` before attempting to build.
Add more GN spew to the `.gitignore` file.
