patch 8.2.2033: Vim9: :def without argument gives compilation error

Problem:    Vim9: :def without argument gives compilation error.
Solution:   Add the DEF instruction. (closes #7344)
diff --git a/src/proto/userfunc.pro b/src/proto/userfunc.pro
index 7ee36db..0029dab 100644
--- a/src/proto/userfunc.pro
+++ b/src/proto/userfunc.pro
@@ -33,6 +33,7 @@
 char_u *printable_func_name(ufunc_T *fp);
 char_u *trans_function_name(char_u **pp, int *is_global, int skip, int flags, funcdict_T *fdp, partial_T **partial);
 char_u *untrans_function_name(char_u *name);
+void list_functions(regmatch_T *regmatch);
 ufunc_T *define_function(exarg_T *eap, char_u *name_arg);
 void ex_function(exarg_T *eap);
 void ex_defcompile(exarg_T *eap);