8411 Build should warn when linking against libraries outside proto area

*** 10,19 ****
--- 10,20 ----
  #
  
  #
  # Copyright 2014 Garrett D'Amore <garrett@damore.org>
  # Copyright 2015 Nexenta Systems, Inc.  All rights reserved.
+ # Copyright 2017 RackTop Systems.
  #
  
  include         $(SRC)/cmd/Makefile.cmd
  include         $(SRC)/cmd/mandoc/Makefile.common
  
*** 28,33 ****
--- 29,37 ----
  clean:
                  $(RM) $(OBJS)
  
  install:        all $(ROOTPROG)
  
+ # Allow zlib to be taken from outside the proto area.
+ $(ADJUNCT_PROTO_NOT_SET)LDFLAGS += $(ZASSERTDEFLIB)=libz.so
+ 
  include         $(SRC)/cmd/Makefile.targ