libkrb5: Add missing KRB5_LIB_FUNCTION/KRB5_LIB_CALL

KRB5_LIB_FUNCTION and KRB5_LIB_CALL are necessary even on private
functions that are exported.

Change-Id: Iccd0cfe87ff0a9d851e29890e9cb55b3ae517ce1

lib/krb5/db_plugin.c

@@ -23,7 +23,7 @@ db_plugins_init(void *arg)
 			     db_plugins_plcallback);
 }
 
-void
+KRB5_LIB_FUNCTION void KRB5_LIB_CALL
 _krb5_load_db_plugins(krb5_context context)
 {
     heim_base_once_f(&db_plugins_once, context, db_plugins_init);