Compilation error on platforms that do not have AtomicU32 from #896

[allanlw]

I hope this is the correct place to file this issue, I'm not too familiar with rust internals.

The recent change #896 adds an import for AtomicU32, but this is not available on the "bpfel-unknown-none" target. This is causing a downstream build issue in aya.

Reproduction:

$ cargo init --lib
    Creating library package
note: see more `Cargo.toml` keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
$ cargo +nightly build --target=bpfel-unknown-none -Z build-std=core --release
   Compiling core v0.0.0 (/home/intr/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)
   Compiling compiler_builtins v0.1.157
   Compiling rustc-std-workspace-core v1.99.0 (/home/intr/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/rustc-std-workspace-core)
error[E0432]: unresolved import `core::sync::atomic::AtomicU32`
 --> /home/intr/.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: `AtomicU64`

For more information about this error, try `rustc --explain E0432`.
error: could not compile `compiler_builtins` (lib) due to 1 previous error

Downstream issue

This can be seen in a real-life example by following the instructions here for setting up an aya template repository, which will fail to build with the same error

[tamird]

@tgross35 flagging this for your consideration.

[tgross35]

Thanks for reporting, this is indeed the correct place. #909 should resolve this.