tests: accommodate a different errno value on HPUX-10.20

* tests/mkdir/selinux: Also handle "Unknown system error".
Reported by Peter Fales.

tests/mkdir/selinux

@@ -37,9 +37,11 @@ for cmd_w_arg in 'mkdir dir' 'mknod b p' 'mkfifo f'; do
   set $cmd_w_arg; cmd=$1
   echo "$cmd: $msg" > exp || fail=1
 
-  # Some systems fail with ENOTSUP, or EINVAL, or even ENOENT.
+  # Some systems fail with ENOTSUP, EINVAL, ENOENT, or even
+  # "Unknown system error".
   sed					\
     -e 's/ Invalid argument$//'		\
+    -e 's/ Unknown system error$//'	\
     -e 's/ Operation not supported$//'	\
     -e 's/ No such file or directory$//' out > k || fail=1
   mv k out || fail=1