build: enhance opam file

sasa.opam

@@ -28,4 +28,5 @@ depopts: [
   "lustre-v6"
   "lutin"
   ]
+build: ["dune" "build" "-p" name "-j" jobs]
 post-messages: ["The last version can be obtained via (opam repo add) http://www-verimag.imag.fr/DIST-TOOLS/SYNCHRONE/opam-repository/ "]