patch 8.2.4038: various code not used when features are disabled

Problem:    Various code not used when features are disabled.
Solution:   Add #ifdefs. (Dominique Pellé, closes #9491)
diff --git a/src/insexpand.c b/src/insexpand.c
index 8fcce7f..51177fb 100644
--- a/src/insexpand.c
+++ b/src/insexpand.c
@@ -263,7 +263,9 @@
 /*
  * Functions to check the current CTRL-X mode.
  */
+#ifdef FEAT_CINDENT
 int ctrl_x_mode_none(void) { return ctrl_x_mode == 0; }
+#endif
 int ctrl_x_mode_normal(void) { return ctrl_x_mode == CTRL_X_NORMAL; }
 int ctrl_x_mode_scroll(void) { return ctrl_x_mode == CTRL_X_SCROLL; }
 int ctrl_x_mode_whole_line(void) { return ctrl_x_mode == CTRL_X_WHOLE_LINE; }