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

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

Change-Id: I63a08af3dc8e9e8f6a63706cbae36ba2a72d3212
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>