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/alloc.c b/src/alloc.c
index cb781b0..3651a2e 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -151,6 +151,7 @@
     return lalloc(size, TRUE);
 }
 
+#if defined(FEAT_QUICKFIX) || defined(PROTO)
 /*
  * alloc() with an ID for alloc_fail().
  */
@@ -163,6 +164,7 @@
 #endif
     return lalloc(size, TRUE);
 }
+#endif
 
 /*
  * Allocate memory and set all bytes to zero.
@@ -178,6 +180,7 @@
     return p;
 }
 
+#if defined(FEAT_SIGNS) || defined(PROTO)
 /*
  * Same as alloc_clear() but with allocation id for testing
  */
@@ -190,6 +193,7 @@
 #endif
     return alloc_clear(size);
 }
+#endif
 
 /*
  * Allocate memory like lalloc() and set all bytes to zero.
@@ -648,6 +652,7 @@
     ga_clear(gap);
 }
 
+#if defined(FEAT_EVAL) || defined(PROTO)
 /*
  * Copy a growing array that contains a list of strings.
  */
@@ -682,6 +687,7 @@
     to->ga_len = from->ga_len;
     return OK;
 }
+#endif
 
 /*
  * Initialize a growing array.	Don't forget to set ga_itemsize and