Maybe include ctype.h.

Treat __cplusplus like __STDC__.
(decls): Use __ in arg names.

lib-src/getopt.h

 /* Declarations for getopt.
-   Copyright (C) 1989,90,91,92,93,94,96,97,98 Free Software Foundation, Inc.
-   NOTE: The canonical source of this file is maintained with the GNU C Library.
-   Bugs can be reported to bug-glibc@gnu.org.
-   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.
+   Copyright (C) 1989-1994, 1996-1999, 2001 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   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.  */
+   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.  */
 
 #ifndef _GETOPT_H
 
@@ -23,6 +22,17 @@
 # define _GETOPT_H 1
 #endif
 
+/* If __GNU_LIBRARY__ is not already defined, either we are being used
+   standalone, or this is the first header included in the source file.
+   If we are being used with glibc, we need to include <features.h>, but
+   that does not exist if we are standalone.  So: if __GNU_LIBRARY__ is
+   not defined, include <ctype.h>, which will pull in <features.h> for us
+   if it's from glibc.  (Why ctype.h?  It's guaranteed to exist and it
+   doesn't flood the namespace with stuff the way some other headers do.)  */
+#if !defined __GNU_LIBRARY__
+# include <ctype.h>
+#endif
+
 #ifdef	__cplusplus
 extern "C" {
 #endif
@@ -82,7 +92,7 @@ extern int optopt;
 
 struct option
 {
-# if defined __STDC__ && __STDC__
+# if (defined __STDC__ && __STDC__) || defined __cplusplus
   const char *name;
 # else
   char *name;
@@ -126,25 +136,26 @@ struct option
    arguments to the option '\0'.  This behavior is specific to the GNU
    `getopt'.  */
 
-#if defined __STDC__ && __STDC__
+#if (defined __STDC__ && __STDC__) || defined __cplusplus
 # ifdef __GNU_LIBRARY__
 /* Many other libraries have conflicting prototypes for getopt, with
    differences in the consts, in stdlib.h.  To avoid compilation
    errors, only prototype getopt for the GNU C library.  */
-extern int getopt (int __argc, char *const *__argv, const char *__shortopts);
+extern int getopt (int ___argc, char *const *___argv, const char *__shortopts);
 # else /* not __GNU_LIBRARY__ */
 extern int getopt ();
 # endif /* __GNU_LIBRARY__ */
 
 # ifndef __need_getopt
-extern int getopt_long (int argc, char *const *argv, const char *__shortopts,
+extern int getopt_long (int ___argc, char *const *___argv,
+			const char *__shortopts,
 		        const struct option *__longopts, int *__longind);
-extern int getopt_long_only (int argc, char *const *argv,
+extern int getopt_long_only (int ___argc, char *const *___argv,
 			     const char *__shortopts,
 		             const struct option *__longopts, int *__longind);
 
 /* Internal only.  Users should not call this directly.  */
-extern int _getopt_internal (int argc, char *const *argv,
+extern int _getopt_internal (int ___argc, char *const *___argv,
 			     const char *__shortopts,
 		             const struct option *__longopts, int *__longind,
 			     int __long_only);