Actually enforce _tf_ssb_assert_not_main_thread.

src/ssb.c

@@ -2270,6 +2270,7 @@ static void _tf_ssb_assert_not_main_thread(tf_ssb_t* ssb)
 		const char* bt = tf_util_backtrace_string();
 		tf_printf("Acquiring DB from the main thread:\n%s\n", bt);
 		tf_free((void*)bt);
+		abort();
 	}
 }