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/main.c b/src/main.c
index dc82a8a..5723d46 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1091,12 +1091,15 @@
     was_safe = FALSE;
 }
 
+#if defined(FEAT_EVAL) || defined(MESSAGE_QUEUE) || defined(PROTO)
     int
 get_was_safe_state(void)
 {
     return was_safe;
 }
+#endif
 
+#if defined(MESSAGE_QUEUE) || defined(PROTO)
 /*
  * Invoked when leaving code that invokes callbacks.  Then trigger
  * SafeStateAgain, if it was safe when starting to wait for a character.
@@ -1137,6 +1140,7 @@
 		  "SafeState: back to waiting, not triggering SafeStateAgain");
 #endif
 }
+#endif
 
 
 /*