Support building all variants. am: 134359c053 am: 46c4de6a93 am: f274137a3d

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/futures-macro/+/1356173

Change-Id: If238a5be6f9e7b253a2d7607127f6f37b3acdba6