New file.

The set_cloexec_flag implementation imported from GNU C Library
Reference Manual.

lib/cloexec.c

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+/* closexec.c - set or clear the close-on-exec descriptor flag
+   Copyright (C) 1991, 2004 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 2, 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, write to the Free Software Foundation,
+   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+
+   The code is taken from glibc/manual/llio.texi  */
+
+#if HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#if HAVE_FCNTL_H
+# include <fcntl.h>
+#endif
+
+#if HAVE_UNISTD_H
+# include <unistd.h>
+#endif
+
+#include "cloexec.h"
+
+#ifndef FD_CLOEXEC
+# define FD_CLOEXEC 1
+#endif
+
+/* Set the `FD_CLOEXEC' flag of DESC if VALUE is nonzero,
+   or clear the flag if VALUE is 0.
+   Return 0 on success, or -1 on error with `errno' set. */
+
+int
+set_cloexec_flag (int desc, int value)
+{
+#if defined F_GETFD && defined F_SETFD
+
+  int flags = fcntl (desc, F_GETFD, 0);
+
+  /* If reading the flags failed, return error indication. */
+  if (flags == -1)
+    return flags;
+
+  /* Set just the flag we want to set. */
+  if (value != 0)
+    flags |= FD_CLOEXEC;
+  else
+    flags &= ~FD_CLOEXEC;
+
+  /* Store modified flags in the descriptor. */
+  return fcntl (desc, F_SETFD, flags);
+
+#else
+
+  return 0;
+
+#endif
+}