3683c43a05
mark sys_common::once::generic::Once::new const-stable
Attempt to address https://github.com/rust-lang/rust/issues/103191 by marking the impl const-stable.
Picked the declaration from the callsite:
21b246587c/library/std/src/sync/once.rs (L67)
This is similar to https://github.com/rust-lang/rust/pull/98457.
With this in, `python3 x.py build library/std --target x86_64-unknown-none` succeeds.