DON'T USE THIS -- Providing some missing POSIX File syscalls.

src/trusted/service_runtime/include/sys/unistd.h

 /*
  * Copyright (c) 2012 The Native Client Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 /*
  * This file is based on the file "newlib/libc/include/sys/unistd.h"
  * from newlib.
  */
@@ skipping 45 matching lines @@
 int     _EXFUN(dup2, (int __fildes, int __fildes2 ));
 #if defined(__CYGWIN__)
 void _EXFUN(endusershell, (void));
 #endif
 int     _EXFUN(execl, (const char *__path, const char *, ... ));
 int     _EXFUN(execle, (const char *__path, const char *, ... ));
 int     _EXFUN(execlp, (const char *__file, const char *, ... ));
 int     _EXFUN(execv, (const char *__path, char * const __argv[] ));
 int     _EXFUN(execve, (const char *__path, char * const __argv[], char * const __envp[] ));
 int     _EXFUN(execvp, (const char *__file, char * const __argv[] ));
-#if defined(__CYGWIN__) || defined(__rtems__) || defined(__SPU__)
 int     _EXFUN(fchdir, (int __fildes));
-#endif
 int     _EXFUN(fchmod, (int __fildes, mode_t __mode ));
 #if !defined(__INSIDE_CYGWIN__)
 int     _EXFUN(fchown, (int __fildes, uid_t __owner, gid_t __group ));
 #endif
 pid_t   _EXFUN(fork, (void ));
 long    _EXFUN(fpathconf, (int __fd, int __name ));
 int     _EXFUN(fsync, (int __fd));
 int     _EXFUN(fdatasync, (int __fd));
 char    _EXFUN(*getcwd, (char *__buf, size_t __size ));
 #if defined(__CYGWIN__)
@@ skipping 294 matching lines @@
 #endif  /* defined(NACL_IN_TOOLCHAIN_HEADERS) */
 
 #ifndef __CYGWIN__
 # define MAXPATHLEN 1024
 #endif
 
 #ifdef __cplusplus
 }
 #endif
 #endif /* NATIVE_CLIENT_SRC_TRUSTED_SERVICE_RUNTIME_INCLUDE_SYS_UNISTD_H_ */