Make entries in dex cache arrays atomic. am: 8c0fcaad77 am: fd71c10c90

Original change: https://android-review.googlesource.com/c/platform/art/+/2469483

Change-Id: I10bf383c59dda4826797dc9a2e9fc3dc6d9e17e2
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>