patch 8.2.2807: build fails with tiny features

Problem:    Build fails with tiny features.
Solution:   Use a dummy function for ex_incdec().

src/ex_docmd.c

@@ -287,6 +287,7 @@ static void	ex_tag_cmd(exarg_T *eap, char_u *name);
 # define ex_endwhile		ex_ni
 # define ex_eval		ex_ni
 # define ex_execute		ex_ni
+# define ex_incdec		ex_ni
 # define ex_finally		ex_ni
 # define ex_finish		ex_ni
 # define ex_function		ex_ni