lguest: expost switcher_pages array (as lg_switcher_pages).

We will need this in page_table.c soon.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index 4c3e532..9a345ef 100644
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -124,6 +124,7 @@
 		       unsigned long addr, unsigned long len);
 void __lgread(struct lg_cpu *, void *, unsigned long, unsigned);
 void __lgwrite(struct lg_cpu *, unsigned long, const void *, unsigned);
+extern struct page **lg_switcher_pages;
 
 /*H:035
  * Using memory-copy operations like that is usually inconvient, so we