xen: fix header export to userspace

scripts/headers_install.pl prevents "__user" from being exported
to userspace headers, so just use compiler.h to make sure that
__user is defined and avoid the error.

unifdef: linux-next-20101112/xx64/usr/include/xen/privcmd.h.tmp: 79: Premature EOF (#if line 33 depth 1)
Signed-off-by: NRandy Dunlap <randy.dunlap@oracle.com>
Cc:	Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc:	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc:	xen-devel@lists.xensource.com (moderated for non-subscribers)
Cc:	virtualization@lists.osdl.org
Cc:	Tony Finch <dot@dotat.at>
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

include/xen/privcmd.h

@@ -34,13 +34,10 @@
 #define __LINUX_PUBLIC_PRIVCMD_H__
 
 #include <linux/types.h>
+#include <linux/compiler.h>
 
 typedef unsigned long xen_pfn_t;
 
-#ifndef __user
-#define __user
-#endif
-
 struct privcmd_hypercall {
 	__u64 op;
 	__u64 arg[5];