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/mark.c b/src/mark.c
index 771eb1b..4765b79 100644
--- a/src/mark.c
+++ b/src/mark.c
@@ -1368,6 +1368,7 @@
 }
 #endif
 
+#if defined(FEAT_VIMINFO) || defined(PROTO)
 /*
  * Return a pointer to the named file marks.
  */
@@ -1376,6 +1377,7 @@
 {
     return namedfm;
 }
+#endif
 
 #if defined(FEAT_EVAL) || defined(PROTO)
 /*