Use modern syscalls for file operations, which operates on file descriptor instead of file name

QT already uses descriptor-oriented syscalls like this:
::fchmod()
::fstat()
::ftruncate()

But lack of using directory syscalls:
::openat ()
::fchdir()
::faccessat()
::fchmodat()
::fchownat()
::fstatat()
::futimesat()
::linkat()
::mkdirat()
::mknodat()
::readlinkat()
::renameat()
::symlinkat()
::unlinkat()
::utimensat()
::mkfifoat()