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

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

Change-Id: I9e0e3f18e7c253d23c07c6645b141218a902ca56
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>