Evaluate XEN_GUEST_HANDLE_64 twice.

This fixes a build error for PV guests (OpenBSD, NetBSD) where the use
of XEN_GUEST_HANDLE_64(uint8_t) leads to a build error because uint8_t
is a #define and not a typedef.

Signed-off-by: Christoph Egger <Christoph.Egger@amd.com>

xen/include/public/arch-x86/xen-x86_32.h

@@ -119,7 +119,8 @@
          (hnd).p = val;                                     \
     } while ( 0 )
 #define uint64_aligned_t uint64_t __attribute__((aligned(8)))
-#define XEN_GUEST_HANDLE_64(name) __guest_handle_64_ ## name
+#define __XEN_GUEST_HANDLE_64(name) __guest_handle_64_ ## name
+#define XEN_GUEST_HANDLE_64(name) __XEN_GUEST_HANDLE_64(name)
 #endif
 
 #ifndef __ASSEMBLY__