ci: add a `v.c can be compiled and run with -os cross` step on the macos job too

.github/workflows/ci.yml

@@ -319,6 +319,13 @@ jobs:
           ./v cmd/tools/test_if_v_test_system_works.v
           ./cmd/tools/test_if_v_test_system_works
 
+      - name: v.c can be compiled and run with -os cross
+        run: |
+          ./v -os cross -o /tmp/v.c cmd/v
+          cc -g -std=gnu11 -w -o v_from_vc /tmp/v.c  -lm -lpthread
+          ls -lart v_from_vc
+          ./v_from_vc version
+
       - name: Self tests
         run: VJOBS=1 ./v -silent test-self