patch 9.0.0623: error for modifying a const is not detected at compile time
Problem: Error for modifying a const is not detected at compile time.
Solution: Add TTFLAG_CONST and check for it in add() and extend().
diff --git a/src/proto/evalfunc.pro b/src/proto/evalfunc.pro
index 5103588..da1c324 100644
--- a/src/proto/evalfunc.pro
+++ b/src/proto/evalfunc.pro
@@ -1,4 +1,5 @@
/* evalfunc.c */
+int arg_type_modifiable(type_T *type, int arg_idx);
char_u *get_function_name(expand_T *xp, int idx);
char_u *get_expr_name(expand_T *xp, int idx);
int find_internal_func(char_u *name);