Fix getopt signature in port_win.h

src/include/win/port_win.h

 /*
  * Copyright 2008, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 122 matching lines @@
 # if !defined(INT64_MIN)
 #  define INT64_MIN      NACL_MIN_VAL(int64_t)
 # endif
 #endif
 #endif  /* _MSC_VER >= 1800 */
 
 EXTERN_C_BEGIN
 
 /* arguments processing */
 int ffs(int x);
-int getopt(int argc, char *argv[], char *optstring);
+int getopt(int argc, char *argv[], const char *optstring);
 extern char *optarg;  /* global argument pointer */
 extern int optind;   /* global argv index */
 
 EXTERN_C_END
 
 
 /*************************** stdio.h  ********************/
 #ifndef NULL
 #if defined(__cplusplus)
 #define NULL    0
 #else
 #define NULL    ((void *)0)
 #endif
 #endif
 
 /************************************************************/
 
 
 /* from linux/limits.h, via sys/param.h */
 #define PATH_MAX 4096
 
 #endif  /* NATIVE_CLIENT_SRC_INCLUDE_WIN_PORT_WIN_H_ */