1. Include a test build (but no link) using g++, to identify errors and warnings before they hit the Windows bots.
2. Move "git diff --quiet" to the end so that the presubmit tests can easily be run before committing locally, if desired.
3. Add "make presubmit" as an alias for "make check-presubmit".
4. Document the individual steps.
BUG= none
R=jpp@chromium.org
Review URL: https://codereview.chromium.org/1453713002 .
