MFC: Add 'compat_freebsd[45]' features corresponding to the kernel options

COMPAT_FREEBSD[45].

sys/kern/kern_mib.c

@@ -38,6 +38,7 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include "opt_compat.h"
 #include "opt_posix.h"
 
 #include <sys/param.h>
@@ -304,6 +305,14 @@ SYSCTL_ULONG(_kern, KERN_HOSTID, hostid, CTLFLAG_RW, &hostid, 0, "Host ID");
 
 SYSCTL_NODE(_kern, OID_AUTO, features, CTLFLAG_RD, 0, "Kernel Features");
 
+#ifdef COMPAT_FREEBSD4
+FEATURE(compat_freebsd4, "Compatible with FreeBSD 4");
+#endif
+
+#ifdef COMPAT_FREEBSD5
+FEATURE(compat_freebsd5, "Compatible with FreeBSD 5");
+#endif
+
 /*
  * This is really cheating.  These actually live in the libc, something
  * which I'm not quite sure is a good idea anyway, but in order for