Import 'lstat' and 'mkstemp' modules from Gnulib.

* lib/mkstemp.c:
* lib/secure_getenv.c:
* lib/tempname.c:
* lib/tempname.h:
* m4/mkstemp.m4:
* m4/secure_getenv.m4:
* m4/tempname.m4: New files.

* lib/Makefile.am:
* m4/gnulib-cache.m4:
* m4/gnulib-comp.m4: Add modules.

lib/secure_getenv.c

@@ -0,0 +1,41 @@
+/* Look up an environment variable more securely.
+
+   Copyright 2013-2014 Free Software Foundation, Inc.
+
+   This program 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 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+#include <stdlib.h>
+
+#if !HAVE___SECURE_GETENV
+# if HAVE_ISSETUGID
+#  include <unistd.h>
+# else
+#  undef issetugid
+#  define issetugid() 1
+# endif
+#endif
+
+char *
+secure_getenv (char const *name)
+{
+#if HAVE___SECURE_GETENV
+  return __secure_getenv (name);
+#else
+  if (issetugid ())
+    return 0;
+  return getenv (name);
+#endif
+}