patch 8.1.0785: depending on the configuration some functions are unused

Problem:    Depending on the configuration some functions are unused.
Solution:   Add more #ifdefs, remove unused functions. (Dominique Pelle,
            closes #3822)
diff --git a/src/misc2.c b/src/misc2.c
index 214a3a2..b1cf8b5 100644
--- a/src/misc2.c
+++ b/src/misc2.c
@@ -1033,6 +1033,7 @@
 /*
  * lalloc() with an ID for alloc_fail().
  */
+#if defined(FEAT_SIGNS) || defined(PROTO)
     char_u *
 lalloc_id(long_u size, int message, alloc_id_T id UNUSED)
 {
@@ -1042,6 +1043,7 @@
 #endif
     return (lalloc((long_u)size, message));
 }
+#endif
 
 #if defined(MEM_PROFILE) || defined(PROTO)
 /*
@@ -2135,6 +2137,7 @@
     return OK;
 }
 
+#if defined(FEAT_EVAL) || defined(FEAT_SEARCHPATH) || defined(PROTO)
 /*
  * For a growing array that contains a list of strings: concatenate all the
  * strings with a separating "sep".
@@ -2170,6 +2173,7 @@
     }
     return s;
 }
+#endif
 
 #if defined(FEAT_VIMINFO) || defined(FEAT_EVAL) || defined(PROTO)
 /*