Fix most warnings that would be caused by gcc flag -Wundef

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5173 c046a42c-6fe2-441c-8c8c-71466251a162
diff --git a/slirp/ip_icmp.c b/slirp/ip_icmp.c
index d1da0a2..53566c1 100644
--- a/slirp/ip_icmp.c
+++ b/slirp/ip_icmp.c
@@ -228,7 +228,7 @@
   /* check msrc */
   if(!msrc) goto end_error;
   ip = mtod(msrc, struct ip *);
-#if DEBUG
+#ifdef DEBUG
   { char bufa[20], bufb[20];
     strcpy(bufa, inet_ntoa(ip->ip_src));
     strcpy(bufb, inet_ntoa(ip->ip_dst));
@@ -285,7 +285,7 @@
   HTONS(icp->icmp_ip.ip_id);
   HTONS(icp->icmp_ip.ip_off);
 
-#if DEBUG
+#ifdef DEBUG
   if(message) {           /* DEBUG : append message to ICMP packet */
     int message_len;
     char *cpnt;