Merge "rust: rust_proc_macro host snapshot support." am: 72cbf588

Original change: https://android-review.googlesource.com/c/platform/build/soong/+/2042225



Change-Id: I2c408bde100546292c09e661ec076d739661e30e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>