Support building all variants. am: 04f52bafb3 am: a67390c7f5 am: ccadfb994b am: 3989d4abf1

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/which/+/1356136

Change-Id: If9c9b32845a85a73e2fffaadfa924ca4cb3d65f8