Update gitignore for in-place build BUG=None TEST=None Change-Id: Ia0782a6643b8d252c95969afd41d701a484df551 Reviewed-on: https://chromium-review.googlesource.com/912188 Commit-Ready: Sean O'Brien <seobrien@chromium.org> Tested-by: Sean O'Brien <seobrien@chromium.org> Reviewed-by: Andrew de los Reyes <adlr@chromium.org>