12310 Add demangle(1) command

*** 12,21 ****
--- 12,22 ----
  #
  # Copyright 2011, Richard Lowe
  # Copyright 2018 Nexenta Systems, Inc.
  # Copyright 2014 Garrett D'Amore <garrett@damore.org>
  # Copyright 2019 OmniOS Community Edition (OmniOSce) Association.
+ # Copyright 2020 Joyent, Inc.
  #
  
  include         $(SRC)/Makefile.master
  
  MANSECT=        1
*** 92,101 ****
--- 93,103 ----
                  ctwatch.1                       \
                  cut.1                           \
                  date.1                          \
                  dc.1                            \
                  deallocate.1                    \
+                 demangle.1                      \
                  deroff.1                        \
                  dhcpinfo.1                      \
                  diff.1                          \
                  diff3.1                         \
                  diffmk.1                        \