ref : build busybox with android bionic libc

Tomorrow's work: build busybox into system (with bionic libc). ref:

1. http://lazyhack.net/compile-busybox-linked-bionic/
2. http://lazyhack.net/cross-compile-busybox-for-android/
3. https://github.com/CyanogenMod/android_external_busybox
4. http://www.iandroid.cn/bbs/viewthread.php?tid=544&extra=page%3D2
5. https://github.com/liudongmiao/busybox-android
6. http://cwhuang.info/2010/03/ad-busybox-source
7. http://blog.csdn.net/codejoker/archive/2010/08/25/5837456.aspx