Use the functions intended for adding Soong config variables. am: 39c9c511cd am: a3a97078a4

Original change: https://android-review.googlesource.com/c/device/generic/art/+/1533263

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I276af8ffeba4d6c2f30ca9b903e394b608975607