Fix compilation of apr-util on darwin by removing dependence on openldap

svn path=/nixpkgs/trunk/; revision=27283

pkgs/development/libraries/apr-util/default.nix

@@ -1,6 +1,6 @@
 { stdenv, fetchurl, apr, expat
 , bdbSupport ? false, db4 ? null
-, ldapSupport ? true, openldap
+, ldapSupport ? !stdenv.isDarwin, openldap
 }:
 
 assert bdbSupport -> db4 != null;