Import structopt-derive-0.4.7 am: dc6194e23f am: eac406d5f2 am: 8af416f386 am: 001ffcbf41

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/structopt-derive/+/1322913

Change-Id: I1e3d5d55a9ba3238e77ea3755f6b2b43c683916e