patch 8.1.1228: not possible to process tags with a function

Problem:    Not possible to process tags with a function.
Solution:   Add tagfunc() (Christian Brabandt, Andy Massimino, closes #4010)
diff --git a/src/globals.h b/src/globals.h
index e3a2c3b..5c5d8d2 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -1067,9 +1067,13 @@
 EXTERN int	postponed_split_flags INIT(= 0);  /* args for win_split() */
 EXTERN int	postponed_split_tab INIT(= 0);  /* cmdmod.tab */
 #ifdef FEAT_QUICKFIX
-EXTERN int	g_do_tagpreview INIT(= 0);  /* for tag preview commands:
-					       height of preview window */
+EXTERN int	g_do_tagpreview INIT(= 0);  // for tag preview commands:
+					    // height of preview window
 #endif
+EXTERN int	g_tag_at_cursor INIT(= FALSE); // whether the tag command comes
+					    // from the command line (0) or was
+					    // invoked as a normal command (1)
+
 EXTERN int	replace_offset INIT(= 0);   /* offset for replace_push() */
 
 EXTERN char_u	*escape_chars INIT(= (char_u *)" \t\\\"|");