Add obstack_printf to libobstack am: 5bef457686 am: c22026c70c am: ffe9223a19 am: eec863e7ee

Original change: https://android-review.googlesource.com/c/platform/external/obstack/+/1843836

Change-Id: I107b36ff2f0fa43ce2daaba02025cc01da2dd56b