patch 8.2.3268: cannot use a block with :autocmd like with :command

Problem:    Cannot use a block with :autocmd like with :command.
Solution:   Add support for a {} block after :autocmd. (closes #8620)
diff --git a/src/proto/usercmd.pro b/src/proto/usercmd.pro
index 9e16a80..e9230d5 100644
--- a/src/proto/usercmd.pro
+++ b/src/proto/usercmd.pro
@@ -10,6 +10,7 @@
 int cmdcomplete_str_to_type(char_u *complete_str);
 char *uc_fun_cmd(void);
 int parse_compl_arg(char_u *value, int vallen, int *complp, long *argt, char_u **compl_arg);
+char_u *may_get_cmd_block(exarg_T *eap, char_u *p, char_u **tofree, int *flags);
 void ex_command(exarg_T *eap);
 void ex_comclear(exarg_T *eap);
 void uc_clear(garray_T *gap);