Fix various build problems on GNU/Hurd.

* grub-core/osdep/unix/getroot.c (strip_extra_slashes): Move inside
!defined (__GNU__).
(xgetcwd): Likewise.
* include/grub/emu/hostdisk.h (grub_util_hurd_get_disk_info)
[__GNU__]: Add prototype.
* util/getroot.c (grub_util_biosdisk_get_grub_dev) [__GNU__]: Format
long int using %ld rather than %d.

grub-core/osdep/unix/getroot.c

@@ -116,6 +116,7 @@
 #include <sys/mount.h>
 #endif
 
+#if !defined (__GNU__)
 static void
 strip_extra_slashes (char *dir)
 {
@@ -155,7 +156,6 @@ xgetcwd (void)
   return path;
 }
 
-#if !defined (__GNU__)
 char **
 grub_util_find_root_devices_from_poolname (char *poolname)
 {