gnulib: add the closeout and secure_getenv modules

* lib/close-stream.c, lib/close-stream.h, lib/closeout.c,
lib/closeout.h, lib/fpending.c, lib/fpending.h, lib/stdio-impl.h,
lib/secure_getenv.c, m4/close-stream.m4, m4/closeout.m4,
m4/fpending.m4, m4/secure_getenv.m4: New file.
* lib/Makefile.am, m4/gnulib-cache.m4, m4/gnulib-comp.m4: Update.

lib/secure_getenv.c

@@ -0,0 +1,54 @@
+/* Look up an environment variable, returning NULL in insecure situations.
+
+   Copyright 2013-2018 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/>.  */
+
+#include <config.h>
+
+#include <stdlib.h>
+
+#if !HAVE___SECURE_GETENV
+# if HAVE_ISSETUGID || (HAVE_GETUID && HAVE_GETEUID && HAVE_GETGID && HAVE_GETEGID)
+#  include <unistd.h>
+# endif
+#endif
+
+char *
+secure_getenv (char const *name)
+{
+#if HAVE___SECURE_GETENV /* glibc */
+  return __secure_getenv (name);
+#elif HAVE_ISSETUGID /* OS X, FreeBSD, NetBSD, OpenBSD */
+  if (issetugid ())
+    return NULL;
+  return getenv (name);
+#elif HAVE_GETUID && HAVE_GETEUID && HAVE_GETGID && HAVE_GETEGID /* other Unix */
+  if (geteuid () != getuid () || getegid () != getgid ())
+    return NULL;
+  return getenv (name);
+#elif defined _WIN32 && ! defined __CYGWIN__ /* native Windows */
+  /* On native Windows, there is no such concept as setuid or setgid binaries.
+     - Programs launched as system services have high privileges, but they don't
+       inherit environment variables from a user.
+     - Programs launched by a user with "Run as Administrator" have high
+       privileges and use the environment variables, but the user has been asked
+       whether he agrees.
+     - Programs launched by a user without "Run as Administrator" cannot gain
+       high privileges, therefore there is no risk. */
+  return getenv (name);
+#else
+  return NULL;
+#endif
+}