Provide local definition of IPPROTO_GRE to allow iptunnel

to build under glibc 2.0.
Make it configurable whether iptunnel & ipmaddr are built,
with the default being off.  This seems to be necessary since
making them work with 2.0 looks hard.  Does it sound
reasonable?

Makefile

@@ -76,7 +76,12 @@
 NET_LIB_PATH = lib
 NET_LIB_NAME = net-tools
 
-PROGS	= ifconfig hostname arp netstat route rarp slattach plipconfig iptunnel ipmaddr
+PROGS	:= ifconfig hostname arp netstat route rarp slattach plipconfig
+
+-include config.make
+ifeq ($(HAVE_IP_TOOLS),1)
+PROGS   += iptunnel ipmaddr
+endif
 
 # Compiler and Linker Options
 # You may need to uncomment and edit these if you are using libc5 and IPv6.

README

@@ -64,7 +64,8 @@ Notable changes since 1.45 include:
  - Various bugs have been fixed.
 
 You need kernel 2.0 or later to use these programs.  These programs
-should compile cleanly with either glibc or libc5.
+should compile cleanly with either glibc or libc5.  The `iptunnel' and
+`ipmaddr' programs require kernel 2.1 or later.
 
 The NLS support was changed from catgets to GNU gettext by Arnaldo
 Carvalho de Melo <acme@conectiva.com.br> in June, 1998, to make the

config.in

@@ -83,3 +83,4 @@ bool '(Cisco)-HDLC/LAPB support' HAVE_HWHDLCLAPB n
 *           Other Features.
 *
 bool 'IP Masquerading support' HAVE_FW_MASQUERADE n
+bool 'Build iptunnel and ipmaddr' HAVE_IP_TOOLS n

configure.sh

@@ -34,6 +34,7 @@
 #
 
 CONFIG=config.h
+MAKECONFIG=config.make
 
 
 [ -z "$BASH" ] && { echo "Configure requires bash" 1>&2; exit 1; }
@@ -69,8 +70,10 @@ function bool()
   done
   if [ "$ans" = "y" ]; then
 	echo "#define $2 1" >>${CONFIG}
+	echo "$2=1" >>${MAKECONFIG}
     else
 	echo "#define $2 0" >>${CONFIG}
+	echo "# $2=0" >> ${MAKECONFIG}
   fi
   raw_input_line="bool '$1' $2 $ans"
   eval "$2=$ans"
@@ -99,6 +102,7 @@ function int()
   #
   > config.new
   > ${CONFIG}
+  > ${MAKECONFIG}
 
   stack=''
   branch='t'

iptunnel.c

@@ -47,6 +47,11 @@
 #undef GRE_VERSION
 #define GRE_VERSION	htons(0x0007)
 
+/* Old versions of glibc do not define this */
+#if __GLIBC__ == 2 && __GLIBC_MINOR__ == 0
+#define IPPROTO_GRE	47
+#endif
+
 #include "utils.h"
 
 static void usage(void) __attribute__((noreturn));