avr-none target fails to build from source on nightly-2025-05-06

[joshlf]

Our attempt to update to nightly-2025-05-06 fails with this error while building with --target=avr-none -Zbuild-std=core:

   Compiling rustc-std-workspace-core v1.99.0 (/home/runner/.rustup/toolchains/nightly-2025-05-06-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/rustc-std-workspace-core)
error[E0432]: unresolved import `core::sync::atomic::AtomicU32`
 --> /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/compiler_builtins-0.1.157/src/math/libm_math/support/feature_detect.rs:3:26
  |
3 | use core::sync::atomic::{AtomicU32, Ordering};
  |                          ^^^^^^^^^
  |                          |
  |                          no `AtomicU32` in `sync::atomic`
  |                          help: a similar name exists in the module: `AtomicU8`

[Urgau]

cc @Patryk27

[Patryk27]

Looking 🔍

[taiki-e]

This is rust-lang/compiler-builtins#908 and the fix will be included in the next nightly (#140724).

[Patryk27]

Yess, was about to write the same, just stumbled upon it 😄