tools-musl/run.sh: restore code accidentally removed

tools-musl/run.sh

@@ -52,6 +52,17 @@ main() {
       prepare_confs ${arch} ${flavor}
     done
   done
+
+  # The parallelization `( do_stages ... ) &` doesn't work here
+  # if catalyst is using snapcache, bug #519656
+  for arch in amd64 i686; do
+    for flavor in hardened vanilla; do
+      (
+        do_stages ${arch} ${flavor}
+        [[ $? == 1 ]] && echo "FAILURE at ${arch} ${flavor} " | tee zzz.log
+      ) &
+    done
+  done
 }
 
 main $1 &