Add jack as a build target for the buildbot.

This avoids dist targets to try on killing the jack server.

Change-Id: Icb913f3ba70ef4c5abd46ebac56cb283e17f0f12
diff --git a/tools/buildbot-build.sh b/tools/buildbot-build.sh
index 047c24f..02787fb 100755
--- a/tools/buildbot-build.sh
+++ b/tools/buildbot-build.sh
@@ -21,7 +21,7 @@
 
 out_dir=${OUT_DIR-out}
 java_libraries_dir=${out_dir}/target/common/obj/JAVA_LIBRARIES
-common_targets="vogar ${java_libraries_dir}/core-tests_intermediates/javalib.jar apache-harmony-jdwp-tests-hostdex ${java_libraries_dir}/jsr166-tests_intermediates/javalib.jar"
+common_targets="vogar ${java_libraries_dir}/core-tests_intermediates/javalib.jar apache-harmony-jdwp-tests-hostdex ${java_libraries_dir}/jsr166-tests_intermediates/javalib.jar ${out_dir}/host/linux-x86/bin/jack"
 mode="target"
 j_arg="-j$(nproc)"
 showcommands=