Rollup merge of #146709 - a4lg:stdarch-sync-20250917, r=Kobzol

stdarch subtree update

Subtree update of `stdarch` to [rust-lang/stdarch@9f12c1a](rust-lang/stdarch@9f12c1a).

Created using https://github.com/rust-lang/josh-sync.

r? ```@Kobzol```

Author: Zalathar