Circle Step 45.1, new functions

• Synced with Circle Step 45.1.
• Implemented functions that previously returned an error code:
  • getcwd() and chdir()
  • dup(), dup2() and fcntl(... F_DUPFD ...) (Note: Only the F_DUPFD command is implemented for fcntl()!)
  • stat() and fstat()
  • fsync()
  • ftruncate()
  • isatty()