buildbot-build.sh: Enable build of both host and target. am: fe1c7b4a5b am: c4251c8631 am: be2f405d00 am: 10ba7f3f49

Original change: https://android-review.googlesource.com/c/platform/art/+/1685634

Change-Id: I60c2290ab1df7da8514743d72cb6484a9b55ad3f