Don't use kern.disks sysctl on PC-98 because the wd driver doesn't call

disk_create() function.

lib/libdisk/disk.c

@@ -456,12 +456,15 @@ Disk_Names()
     struct diskslices ds;
     int fd;
     static char **disks;
+#ifndef PC98
     int error;
     size_t listsize;
     char *disklist, **dp;
+#endif
 
     disks = malloc(sizeof *disks * (1 + MAX_NO_DISKS));
     memset(disks,0,sizeof *disks * (1 + MAX_NO_DISKS));
+#ifndef PC98
     error = sysctlbyname("kern.disks", NULL, &listsize, NULL, 0);
     if (!error) {
 	    disklist = (char *)malloc(listsize);
@@ -473,6 +476,7 @@ Disk_Names()
 	    return disks;
     }
     warn("kern.disks sysctl not available");
+#endif
     k = 0;
 	for (j = 0; device_list[j]; j++) {
 		for (i = 0; i < MAX_NO_DISKS; i++) {