Add librusb_platform variant am: 56e2703977

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/rusb/+/3375753

Change-Id: Ib9af3e1d855bf2b754e5db555fad4a2e322b5c28
Signed-off-by: Automerger Merge Worker <[email protected]>