patch 8.1.1800: function call functions have too many arguments

Problem:    Function call functions have too many arguments.
Solution:   Pass values in a funcexe_T struct.

src/structs.h

@@ -1517,6 +1517,22 @@ struct funccall_S
 				// "func"
 };
 
+// Struct passed between functions dealing with function call execution.
+//
+// "argv_func", when not NULL, can be used to fill in arguments only when the
+// invoked function uses them.  It is called like this:
+//   new_argcount = argv_func(current_argcount, argv, called_func_argcount)
+//
+typedef struct {
+    int		(* argv_func)(int, typval_T *, int);
+    linenr_T	firstline;	// first line of range
+    linenr_T	lastline;	// last line of range
+    int		*doesrange;	// if not NULL: return: function handled range
+    int		evaluate;	// actually evaluate expressions
+    partial_T	*partial;	// for extra arguments
+    dict_T	*selfdict;	// Dictionary for "self"
+} funcexe_T;
+
 /*
  * Struct used by trans_function_name()
  */