Add option to add dist build target.

For use in CI to collect build logs etc.

Test: art/tools/buildbot-build.sh --dist
      Check that out/dist/logs is created with some logs
Bug: 232915534
Change-Id: I8e3d80d673ae726f4b2f1fb69f2af7cb6b5f16db
diff --git a/tools/buildbot-build.sh b/tools/buildbot-build.sh
index 44fe5de..77eac77 100755
--- a/tools/buildbot-build.sh
+++ b/tools/buildbot-build.sh
@@ -69,6 +69,9 @@
   elif [[ "$1" == "--showcommands" ]]; then
     showcommands="showcommands"
     shift
+  elif [[ "$1" == "--dist" ]]; then
+    common_targets="$common_targets dist"
+    shift
   elif [[ "$1" == "" ]]; then
     break
   else