FreeBSD build fix.

Author: brndnmtthws

src/freebsd.h

@@ -41,6 +41,8 @@
 #include <machine/apm_bios.h>
 #endif /* i386 || __i386__ */
 
+extern kvm_t *kd;
+
 int get_entropy_avail(unsigned int *);
 int get_entropy_poolsize(unsigned int *);
 void print_sysctlbyname(struct text_object *, char *, unsigned int);