fix(tvix/eval): preserve catchables in nix_cmp_ordering(), fix b/338

This commit fixes b/338 by properly propagating catchables through
comparison operations.

Change-Id: I6b0283a40f228ecf9a6398d24c060bdacb1077cf
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10221
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
Autosubmit: Adam Joseph <adam@westernsemico.com>

tvix/eval/src/vm/macros.rs

@@ -44,7 +44,10 @@ macro_rules! cmp_op {
             let b = generators::request_force(&co, b).await;
             let span = generators::request_span(&co).await;
             let ordering = a.nix_cmp_ordering(b, co, span).await?;
-            Ok(Value::Bool(cmp_op!(@order $op ordering)))
+            match ordering {
+                Err(cek) => Ok(Value::Catchable(cek)),
+                Ok(ordering) => Ok(Value::Bool(cmp_op!(@order $op ordering))),
+            }
         }
 
         let gen_span = $frame.current_light_span();