Add a define for NFS_SUPER_MAGIC

Commit 3c12a67b added
a dependency on the NFS_SUPER_MAGIC macro, which is
defined in linux/magic.h.  Unfortunately linux/magic.h
is not available in RHEL-5, and causes a compile error.
Just define it locally, since this is something that
can't change.
Signed-off-by: NChris Lalancette <clalance@redhat.com>

src/qemu/qemu_driver.c

@@ -49,8 +49,10 @@
 
 #ifdef __linux__
 #include <sys/vfs.h>
-#include <linux/magic.h>
-#endif
+#ifndef NFS_SUPER_MAGIC
+#define NFS_SUPER_MAGIC 0x6969
+#endif /* NFS_SUPER_MAGIC */
+#endif /* __linux__ */
 
 #include "virterror_internal.h"
 #include "logging.h"