ci: Test loom under no-default-features

This commit adds loom tests to CI with --no-default-features, then also
fixes a compile error that was introduced in a new version of loom.

Closes #64

.github/workflows/ci.yml

@@ -107,6 +107,11 @@ jobs:
         env:
           RUSTFLAGS: "--cfg=loom"
           LOOM_MAX_PREEMPTIONS: 4
+      - name: Loom tests without default features
+        run: cargo test --release --test loom --features loom --no-default-features 
+        env:
+          RUSTFLAGS: "--cfg=loom"
+          LOOM_MAX_PREEMPTIONS: 4
 
   security_audit:
     permissions:

src/sync.rs

@@ -36,6 +36,9 @@ mod sync_impl {
         pub(crate) use loom::sync::atomic::*;
     }
 
+    #[cfg(not(feature = "std"))]
+    pub(crate) use loom::hint::spin_loop;
+    #[cfg(feature = "std")]
     pub(crate) use loom::thread::yield_now;
 }