Print any start-up exceptions in Session's constructor, so custom main's don't need to worry about them

include/internal/catch_session.h

@@ -45,6 +45,7 @@ namespace Catch {
         clara::Parser m_cli;
         ConfigData m_configData;
         std::shared_ptr<Config> m_config;
+        bool m_startupExceptions = false;
     };
 
 } // end namespace Catch