Bump `stdarch` This bumps `stdarch` to https://github.com/rust-lang/stdarch/commit/684de0d6fef708cae08214fef9643dd9ec7296e1 to get in https://github.com/rust-lang/stdarch/pull/1677 (tracked in https://github.com/rust-lang/rust/issues/133908). From the [commit history](https://github.com/rust-lang/stdarch/compare/e5e00aab0a8c8fa35fb7865e88fa82366f615c53...684de0d6fef708cae08214fef9643dd9ec7296e1) I deduced that there shouldn't be any changes to Rust necessary. From past PRs I'm assuming that bumping `stdarch` like this is fine, but please let me know if this is somehow inappropriate or requires something more to be done! try-job: arm-android try-job: armhf-gnu