Merge "Update futures-macro to 0.3.21" am: 4880177011 am: 0a18d3da78 am: 1c96ed3fa7 am: a2e0086b1a am: 44b5d5b5c3

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/futures-macro/+/2005113

Change-Id: Ib28fd4e948a6a8a29e456b04a5179f4883b5f1d4