Add go/android3p files for external/obstack am: 3f150c198b am: 2437e11c64 am: 839fae7fee

Original change: https://android-review.googlesource.com/c/platform/external/obstack/+/1843834

Change-Id: If52e62345b0a7df40dab14df8ab5c53b0113c57f