Add support for product-specific build flags am: c6631fed am: ec7a1e3a am: cffa1db8

Original change: https://android-review.googlesource.com/c/platform/build/+/2787001



Change-Id: I4576a78fa7c73dbe5decf1075dc76650ba2a9445
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>