Use onbld mandoc.

*** 944,953 ****
--- 944,955 ----
  #
  # This is only used during the -t tools build
  #
  opt/onbld/bin/i386/elfsign      i386
  opt/onbld/bin/sparc/elfsign     sparc
+ opt/onbld/bin/i386/mandoc       i386
+ opt/onbld/bin/sparc/mandoc      sparc
  
  #
  # Private libdwarf
  #
  opt/onbld/lib/i386/libdwarf.so  i386