Make exit unreachable a verification failures

Signed-off-by: Alan Jowett <[email protected]>

src/crab_verifier.cpp

@@ -100,7 +100,7 @@ static checks_db generate_report(cfg_t& cfg, const crab::invariant_table_t& pre_
 
          // Check if the exit is unreachable, which could indicate an infinite loop
         if (last_inv.is_bottom()) {
-            m_db.add_unreachable(label_t::exit, "Exit is unreachable.");
+            m_db.add_warning(label_t::exit, "Exit is unreachable.");
         }
     }