Merge "c2a: Support customizing rustc" am: b037e85818 am: 18a3ef5f8e am: 97e5b7be32

Original change: https://android-review.googlesource.com/c/platform/development/+/2633771

Change-Id: I3ecaaa93a89703a6c3d20c81210f7c6683c145fb
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>