Merge "c2a: Support customizing rustc" am: b037e85818

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

Change-Id: I37abc96ed8cae28bf654e425713eda1a6c3ec67d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>