patch 8.2.4981: it is not possible to manipulate autocommands

Problem:    It is not possible to manipulate autocommands.
Solution:   Add functions to add, get and set autocommands. (Yegappan
            Lakshmanan, closes #10291)
diff --git a/src/proto/autocmd.pro b/src/proto/autocmd.pro
index ddf3915..713ae24 100644
--- a/src/proto/autocmd.pro
+++ b/src/proto/autocmd.pro
@@ -38,4 +38,7 @@
 char_u *get_event_name(expand_T *xp, int idx);
 int autocmd_supported(char_u *name);
 int au_exists(char_u *arg);
+void f_autocmd_add(typval_T *argvars, typval_T *rettv);
+void f_autocmd_delete(typval_T *argvars, typval_T *rettv);
+void f_autocmd_get(typval_T *argvars, typval_T *rettv);
 /* vim: set ft=c : */