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/proto/gui_xim.pro b/src/proto/gui_xim.pro
index 2e944ae..bac7321 100644
--- a/src/proto/gui_xim.pro
+++ b/src/proto/gui_xim.pro
@@ -1,6 +1,6 @@
 /* gui_xim.c */
-char *set_imactivatefunc_option(void);
-char *set_imstatusfunc_option(void);
+char *did_set_imactivatefunc(optset_T *args);
+char *did_set_imstatusfunc(optset_T *args);
 void free_xim_stuff(void);
 int set_ref_in_im_funcs(int copyID);
 void im_set_active(int active);