Linaro busybox
http://android.git.linaro.org/gitweb?p=platform/external/busybox.git;a=summary
git clone git://android.git.linaro.org/platform/external/busybox.git
Android.mkがないですが...
https://blueprints.launchpad.net/linaro-android/+spec/linaro-android-include-busybox