internal/syscall/unix: add constants for hurd

Patch by Svante Signell.

Change-Id: I44cd3507da15928d9ed6e466a7cdbf33552d17b0
Reviewed-on: https://go-review.googlesource.com/c/161517
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/libgo/go/internal/syscall/unix/at_sysnum_hurd.go b/libgo/go/internal/syscall/unix/at_sysnum_hurd.go
new file mode 100644
index 0000000..223eb42
--- /dev/null
+++ b/libgo/go/internal/syscall/unix/at_sysnum_hurd.go
@@ -0,0 +1,8 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package unix
+
+const AT_REMOVEDIR = 0x200
+const AT_SYMLINK_NOFOLLOW = 0x100