Merge "Clarify the defines documentation further." am: 1441748956 am: 17b5bb88c1

Original change: https://android-review.googlesource.com/c/platform/bionic/+/2595593

Change-Id: If9f1f6ba83a045663508c64d473af83908fad51f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>