asm/system.h header doesn't exist anymore. It isn't a bug in kernel
headers exported to userspace, since system.h includes linux spefic
code (like alternatives patching), and also I think isn't task of linux
kernel to define generic macros for userspace to use, like mb. So define
our own version of mb, the same way/based on
/usr/include/alsa/iatomic.h from alsa-lib (libalsa2-devel)

diff -p -up fwmon-1.1.0/sniffer.c.orig fwmon-1.1.0/sniffer.c
--- fwmon-1.1.0/sniffer.c.orig	2008-01-09 12:09:07.000000000 -0500
+++ fwmon-1.1.0/sniffer.c	2008-01-09 12:24:38.000000000 -0500
@@ -27,7 +27,6 @@ static const char rcsid[]=
 #include <sys/poll.h>
 #include <sys/mman.h>
 #include <sys/ioctl.h>
-#include <asm/system.h>
 #include <linux/sockios.h>
 
 #include <features.h>
@@ -40,6 +39,47 @@ static const char rcsid[]=
 # include <linux/if_ether.h>
 #endif
 
+#if defined(__i386__)
+#define mb()	__asm__ __volatile__ ("lock; addl $0,0(%%esp)":::"memory")
+#endif
+
+#if defined(__x86_64__)
+#define mb()	__asm__ __volatile__ ("mfence":::"memory")
+#endif
+
+#if defined(__ia64__)
+#define mb()	__asm__ __volatile__ ("mf":::"memory")
+#endif
+
+#if defined(__alpha__)
+#define mb()	__asm__ __volatile__("mb":::"memory")
+#endif
+
+#if defined(__powerpc__)
+#define mb()	__asm__ __volatile__ ("sync":::"memory")
+#endif
+
+#if defined(__mips__)
+#define mb()						\
+__asm__ __volatile__(					\
+	"# prevent instructions being moved around\n\t"	\
+	".set\tnoreorder\n\t"				\
+	"# 8 nops to fool the R4400 pipeline\n\t"	\
+	"nop;nop;nop;nop;nop;nop;nop;nop\n\t"		\
+	".set\treorder"					\
+	: /* no output */				\
+	: /* no input */				\
+	: "memory")
+#endif
+
+#if defined(__arm__)
+#define mb() __asm__ __volatile__ ("":::"memory")
+#endif
+
+#ifndef mb
+#define mb()
+#endif
+
 int frames;
 int sniff_fd=-1;
 char *map=NULL;