Clarify that is_shared in practice gives access to system libs for am: 81b3f56cab am: 920ec80154

Original change: https://android-review.googlesource.com/c/platform/art/+/2214689

Change-Id: I5eb636a422c579ec459e51166d89924b3dc57bd8
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>