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

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

Change-Id: Id42593b6e678a73f21486b675bd1c8806bc0c037
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>