patch 8.0.1595: no autocommand triggered before exiting

Problem:    No autocommand triggered before exiting.
Solution:   Add the ExitPre autocommand event.
diff --git a/src/Makefile b/src/Makefile
index 1b13aa9..905e3f1 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -2155,6 +2155,7 @@
 	test_eval_stuff \
 	test_ex_undo \
 	test_ex_z \
+	test_exit \
 	test_exec_while_if \
 	test_execute_func \
 	test_exists \