patch 9.0.1330: handling new value of an option has a long "else if" chain

Problem:    Handling new value of an option has a long "else if" chain.
Solution:   Use a function pointer. (Yegappan Lakshmanan, closes #12015)
diff --git a/src/ex_getln.c b/src/ex_getln.c
index b2bf4ed..a938bd6 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -4366,7 +4366,7 @@
  * Returns NULL if value is OK, error message otherwise.
  */
     char *
-check_cedit(void)
+did_set_cedit(optset_T *args UNUSED)
 {
     int n;