<sys/stat.h>: Use Linux UAPI header for statx if available and useful

This will automatically import new STATX_* constants.  It also avoids
a conflict between <sys/stat.h> and <linux/stat.h>.

io/bits/statx-generic.h

@@ -0,0 +1,60 @@
+/* Generic statx-related definitions and declarations.
+   Copyright (C) 2018-2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* This interface is based on <linux/stat.h> in Linux.  */
+
+#ifndef _SYS_STAT_H
+# error Never include <bits/statx-generic.h> directly, include <sys/stat.h> instead.
+#endif
+
+#include <bits/types/struct_statx_timestamp.h>
+#include <bits/types/struct_statx.h>
+
+#ifndef STATX_TYPE
+# define STATX_TYPE 0x0001U
+# define STATX_MODE 0x0002U
+# define STATX_NLINK 0x0004U
+# define STATX_UID 0x0008U
+# define STATX_GID 0x0010U
+# define STATX_ATIME 0x0020U
+# define STATX_MTIME 0x0040U
+# define STATX_CTIME 0x0080U
+# define STATX_INO 0x0100U
+# define STATX_SIZE 0x0200U
+# define STATX_BLOCKS 0x0400U
+# define STATX_BASIC_STATS 0x07ffU
+# define STATX_ALL 0x0fffU
+# define STATX_BTIME 0x0800U
+# define STATX__RESERVED 0x80000000U
+
+# define STATX_ATTR_COMPRESSED 0x0004
+# define STATX_ATTR_IMMUTABLE 0x0010
+# define STATX_ATTR_APPEND 0x0020
+# define STATX_ATTR_NODUMP 0x0040
+# define STATX_ATTR_ENCRYPTED 0x0800
+# define STATX_ATTR_AUTOMOUNT 0x1000
+#endif /* !STATX_TYPE */
+
+__BEGIN_DECLS
+
+/* Fill *BUF with information about PATH in DIRFD.  */
+int statx (int __dirfd, const char *__restrict __path, int __flags,
+           unsigned int __mask, struct statx *__restrict __buf)
+  __THROW __nonnull ((2, 5));
+
+__END_DECLS