Support building all variants. am: 134359c053 am: 46c4de6a93 am: f274137a3d am: ca0a38e417

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

Change-Id: Ie7f70f0b8a00334ac1a8fab1616dc5579d131e98