Use onbld mandoc.

@@ -9,14 +9,14 @@
 # at http://www.illumos.org/license/CDDL.
 #
 
 #
 # Copyright 2011, Richard Lowe
-# Copyright 2013 Nexenta Systems, Inc.  All rights reserved.
+# Copyright 2014 Nexenta Systems, Inc.  All rights reserved.
 #
 
-MANDOC=         $(ROOT)/usr/bin/mandoc
+MANDOC=         $(ONBLD_TOOLS)/bin/${MACH}/mandoc
 ROOTMAN=        $(ROOT)/usr/share/man
 ROOTHASMAN=     $(ROOT)/usr/has/man
 FILEMODE=       0444
 
 # The manual section being built, client Makefiles must set this to, for e.g.