include mutex

Signed-off-by: Nikolaj Bjorner <[email protected]>

src/sat/smt/sls_solver.h

@@ -17,6 +17,7 @@ Module Name:
 #pragma once
 
 #include <thread>
+#include <mutex>
 #include "util/rlimit.h"
 #include "ast/sls/bv_sls.h"
 #include "sat/smt/sat_th.h"