initial pass at using derivatives in regex unfolding

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/smt/CMakeLists.txt

@@ -13,10 +13,11 @@ z3_add_component(smt
     old_interval.cpp
     qi_queue.cpp
     seq_axioms.cpp
-    seq_skolem.cpp
     seq_eq_solver.cpp
     seq_ne_solver.cpp
     seq_offset_eq.cpp
+    seq_regex.cpp
+    seq_skolem.cpp
     seq_unicode.cpp
     smt_almost_cg_table.cpp
     smt_arith_value.cpp