add option to "rotate" cores during core finding

enable to find multiple cores in a round and at the same time facilitate rotation around satisfiable subsets to explore neighborhoods for improved assignments.

src/opt/CMakeLists.txt

@@ -5,6 +5,7 @@ z3_add_component(opt
     maxsmt.cpp
     opt_cmds.cpp
     opt_context.cpp
+    opt_cores.cpp
     opt_lns.cpp
     opt_pareto.cpp
     opt_parse.cpp