refactor(users/edef/weave): use swap rather than CAS

We only care about ordering on the same variable, and we rely on the
release barrier provided by rayon's thread joining.

The comparison failing is always an error path, and we're indifferent
about which thread it fails on.

Change-Id: I592a7eaae5b6935cf424c6576a49786f39909fb6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12666
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

users/edef/weave/src/main.rs

@@ -43,9 +43,11 @@ fn main() -> Result<()> {
         eprint!("… resolve roots\r");
         ph_array.par_iter().enumerate().for_each(|(idx, h)| {
             if let Some(idx_slot) = roots.find(h) {
-                idx_slot
-                    .compare_exchange(INDEX_NULL, idx as u32, Ordering::SeqCst, Ordering::SeqCst)
-                    .expect("duplicate entry");
+                assert_eq!(
+                    idx_slot.swap(idx as u32, Ordering::Relaxed),
+                    INDEX_NULL,
+                    "duplicate entry"
+                );
             }
         });
         eprintln!("{DONE}");