Use dune -x instead of a rule to compile the cosmopolitan example

.github/workflows/esperanto.yml

@@ -27,7 +27,7 @@ jobs:
       run: opam install opam-monorepo
     - name: Add opam-monorepo overlays
       run: opam repo add dune-universe git+https://github.com/dune-universe/opam-overlays.git
-    - name: Example with LWT & Esperanto
+    - name: Example with lwt & esperanto
       run: |
         mkdir esperanto-example
         cd esperanto-example
@@ -70,13 +70,6 @@ jobs:
         (executable
          (name cat)
          (libraries lwt.unix))
-
-        (rule
-         (target cat.com)
-         (enabled_if (= %{context_name} esperanto))
-         (mode promote)
-         (deps cat.exe)
-         (action (run objcopy -S -O binary %{deps} %{target})))
         EOF
         cat >cat.opam <<EOF
         opam-version: "2.0"
@@ -106,5 +99,6 @@ jobs:
         EOF
         opam monorepo lock --ocaml-version  ${{ matrix.ocaml-version }}
         opam monorepo pull
-        opam exec -- dune build ./cat.com
+        opam exec -- dune build -x esperanto ./cat.exe
+        objcopy -S -O binary _build/default.esperanto/cat.exe cat.com
         ./cat.com < cat.ml