Fix -Wundef warning.  Upstream addressed this differently via:

commit a4ccbc9b243926a9904624b387fb18583c3d4d4d
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Wed Jun 25 16:39:33 2014 +0000

    Remove __ASSUME_XFS_RESTRICTED_CHOWN.

diff --git a/sysdeps/unix/sysv/linux/pathconf.c b/sysdeps/unix/sysv/linux/pathconf.c
index febdc3731119bfce..0ed2abb9cb1d618d 100644
--- a/sysdeps/unix/sysv/linux/pathconf.c
+++ b/sysdeps/unix/sysv/linux/pathconf.c
@@ -284,7 +284,7 @@ __statfs_chown_restricted (int result, const struct statfs *fsbuf)
       return -1;
     }
 
-#if __ASSUME_XFS_RESTRICTED_CHOWN
+#ifdef __ASSUME_XFS_RESTRICTED_CHOWN
   return 1;
 #else
   int fd;