Use onbld mandoc.

@@ -51,11 +51,12 @@
 
 #
 #  special versions of commands for use only in build
 #
 UNSHIPPED_SUBDIRS = \
-        elfsign
+        elfsign \
+        mandoc
 
 sparc_SUBDIRS= \
         chk4ubin \
         stabs \
         tokenize