UNIX98 requires unistd.h for getopt, and requires -D_XOPEN_SOURCE=500.

*** 23,33 ****
  # Makefile for "ifparse" 
  #
  # Copyright 2000-2003 Sun Microsystems, Inc.  All rights reserved.
  # Use is subject to license terms.
  #
! # ident "%Z%%M% %I%     %E% SMI"
  #
  
  PROG =          ifparse
  ROOTFS_PROG =   $(PROG)
  OBJS=           ifparse.o
--- 23,33 ----
  # Makefile for "ifparse" 
  #
  # Copyright 2000-2003 Sun Microsystems, Inc.  All rights reserved.
  # Use is subject to license terms.
  #
! # Copyright 2014 Garrett D'Amore <garrett@damore.org>
  #
  
  PROG =          ifparse
  ROOTFS_PROG =   $(PROG)
  OBJS=           ifparse.o
*** 38,49 ****
  
  CPPFLAGS += -I$(CMDINETCOMMONDIR)
  LINTFLAGS +=    -m
  
  # these #defines are required to use UNIX 98 interfaces
! $(OBJS)         := CPPFLAGS +=-D_POSIX_C_SOURCE 
! LINTFLAGS       += -D_POSIX_C_SOURCE -I$(CMDINETCOMMONDIR)
  
  .KEEP_STATE:
  
  all:    $(ROOTFS_PROG)
  
--- 38,49 ----
  
  CPPFLAGS += -I$(CMDINETCOMMONDIR)
  LINTFLAGS +=    -m
  
  # these #defines are required to use UNIX 98 interfaces
! $(OBJS)         := CPPFLAGS +=-D_XOPEN_SOURCE=500       
! LINTFLAGS       += -D_XOPEN_SOURCE=500 -I$(CMDINETCOMMONDIR)
  
  .KEEP_STATE:
  
  all:    $(ROOTFS_PROG)