Cannot build --no-default-features --features loom --cfg loom

[jbr]

Discovered while working on smol-rs/event-listener#126

RUSTFLAGS="--cfg=loom" cargo build --no-default-features --features loom
   Compiling concurrent-queue v2.4.0 (/Users/jbr/code/concurrent-queue)
error[E0425]: cannot find function `spin_loop` in this scope
  --> src/sync.rs:51:5
   |
51 |     spin_loop();
   |     ^^^^^^^^^ not found in this scope
   |
help: consider importing one of these items
   |
42 + use core::hint::spin_loop;
   |
42 + use loom::hint::spin_loop;
   |

warning: unused import: `loom::thread::yield_now`
  --> src/sync.rs:39:20
   |
39 |     pub(crate) use loom::thread::yield_now;
   |                    ^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(unused_imports)]` on by default

For more information about this error, try `rustc --explain E0425`.
warning: `concurrent-queue` (lib) generated 1 warning
error: could not compile `concurrent-queue` (lib) due to 1 previous error; 1 warning emitted