applied patch for FreeBSD by Julio Merino, closing #104475 Daniel

* xmlcatalog.c xmllint.c: applied patch for FreeBSD by
  Julio Merino, closing #104475
Daniel
diff --git a/xmlcatalog.c b/xmlcatalog.c
index 5b6ceaf..1830f5e 100644
--- a/xmlcatalog.c
+++ b/xmlcatalog.c
@@ -41,7 +41,9 @@
 
 #ifdef LIBXML_CATALOG_ENABLED
 
+#ifndef XML_SGML_DEFAULT_CATALOG
 #define XML_SGML_DEFAULT_CATALOG "/etc/sgml/catalog"
+#endif
 
 /************************************************************************
  * 									*