patch 9.1.1391: Vim does not have a vertical tabpanel

Problem:  Vim does not have a tabpanel
Solution: include the tabpanel feature
          (Naruhiko Nishino, thinca)

closes: #17263

Co-authored-by: thinca <thinca@gmail.com>
Signed-off-by: Naruhiko Nishino <naru123456789@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/proto/optionstr.pro b/src/proto/optionstr.pro
index 4c4ec3e..84dd1fb 100644
--- a/src/proto/optionstr.pro
+++ b/src/proto/optionstr.pro
@@ -1,4 +1,6 @@
 /* optionstr.c */
+char *did_set_tabpanelopt(optset_T *args);
+int expand_set_tabpanelopt(optexpand_T *args, int *numMatches, char_u ***matches);
 void didset_string_options(void);
 void trigger_optionset_string(int opt_idx, int opt_flags, char_u *oldval, char_u *oldval_l, char_u *oldval_g, char_u *newval);
 void check_buf_options(buf_T *buf);