selinux-h: add stubs for selabel_open etc.

Coreutils with --enable-gcc-warnings does not build on Ubuntu 20.10
because matchpathcon is deprecated in favor of selabel_open etc.,
so this patch adds stubs for these functions.
* lib/se-label.c, lib/se-label.in.h, m4/selinux-label-h.m4: New files.
* lib/se-selinux.in.h (struct selinux_opt): Add incomplete decl,
as it is needed for selabel_open and selinux/selinux.h declares
this type here.
* modules/selinux-h (Files): Add the new files.
(configure.ac): Add gl_HEADERS_SELINUX_LABEL_H.
(lib_SOURCES): Add se-label.in.h, se-label.c.
(BUILT_SOURCES): Add $(SELINUX_LABEL_H).
(selinux/label.h): New rule, mimicking selinux/context.h.
(MOSTLYCLEANFILES): Add selinux/label.h, selinux/label.h-t.
(Include): Add selinux/label.h.

3 files changed, 63 insertions, 0 deletions

diff --git a/lib/se-label.c b/lib/se-label.c
new file mode 100644
index 0000000000..16d706fd89
--- /dev/null
+++ b/lib/se-label.c
@@ -0,0 +1,3 @@
+#include <config.h>
+#define SE_LABEL_INLINE _GL_EXTERN_INLINE
+#include <selinux/label.h>
diff --git a/lib/se-label.in.h b/lib/se-label.in.h
new file mode 100644
index 0000000000..405e77401c
--- /dev/null
+++ b/lib/se-label.in.h
@@ -0,0 +1,59 @@
+/* Replacement <selinux/label.h> for platforms that lack it.
+   Copyright 2020 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Paul Eggert.  */
+
+#ifndef SELINUX_LABEL_H
+
+#define SELINUX_LABEL_H
+
+#include <selinux/selinux.h>
+#include <errno.h>
+
+#ifndef _GL_INLINE_HEADER_BEGIN
+ #error "Please include config.h first."
+#endif
+_GL_INLINE_HEADER_BEGIN
+#ifndef SE_LABEL_INLINE
+# define SE_LABEL_INLINE _GL_INLINE
+#endif
+
+/* The definition of _GL_UNUSED_PARAMETER is copied here.  */
+
+#define SELABEL_CTX_FILE 0
+
+struct selabel_handle;
+
+SE_LABEL_INLINE int
+selabel_lookup (struct selabel_handle *hnd _GL_UNUSED_PARAMETER,
+                char **context _GL_UNUSED_PARAMETER,
+                char const *key _GL_UNUSED_PARAMETER,
+                int type _GL_UNUSED_PARAMETER)
+{ errno = ENOTSUP; return -1; }
+
+SE_LABEL_INLINE struct selabel_handle *
+selabel_open (int backend _GL_UNUSED_PARAMETER,
+              struct selinux_opt *options _GL_UNUSED_PARAMETER,
+              unsigned nopt _GL_UNUSED_PARAMETER)
+{ errno = ENOTSUP; return 0; }
+
+SE_LABEL_INLINE void
+selabel_close (struct selabel_handle *hnd _GL_UNUSED_PARAMETER)
+{ errno = ENOTSUP; }
+
+_GL_INLINE_HEADER_END
+
+#endif
diff --git a/lib/se-selinux.in.h b/lib/se-selinux.in.h
index 022596bb85..a6c194aa0e 100644
--- a/lib/se-selinux.in.h
+++ b/lib/se-selinux.in.h
@@ -43,6 +43,7 @@ _GL_INLINE_HEADER_BEGIN
 #  if !GNULIB_defined_security_types
 
 typedef unsigned short security_class_t;
+struct selinux_opt;
 #   define is_selinux_enabled() 0
 
 SE_SELINUX_INLINE int