message: Finalize Aarch64 support
  Update platform support for linux to avoid the use of syscalls not
  supported by Aarch64.
  - link, chown, and open should use fchownat and linkat with fd
  set to AT_FDCWD.
  - use dup3 with the 3rd arg set to 0 instead of dup2.
diff: @@ -18,7 +18,7 @@ pub fn chdir(path: *const c_char) -> c_int {
  }
  pub fn chown(path: *const c_char, owner: uid_t, group: gid_t) -> c_int {
  - unsafe { syscall!(CHOWN, owner as u32, group as u32) as c_int }
  + unsafe { syscall!(FCHOWNAT, AT_FDCWD, path, owner as u32, group as u32) as c_int }
  }
  pub fn close(fildes: c_int) -> c_int {
  @@ -30,7 +30,7 @@ pub fn dup(fildes: c_int) -> c_int {
  }
  pub fn dup2(fildes: c_int, fildes2: c_int) -> c_int {
  - unsafe { syscall!(DUP2, fildes, fildes2) as c_int }
  + unsafe { syscall!(DUP3, fildes, fildes2, 0) as c_int }
  }
  pub fn exit(status: c_int) -> ! {
  @@ -92,15 +92,9 @@ pub fn getuid() -> uid_t {
  }
  pub fn link(path1: *const c_char, path2: *const c_char) -> c_int {
  - unsafe { syscall!(LINK, path1, path2) as c_int }
  + unsafe { syscall!(LINKAT, AT_FDCWD, path1, path2) as c_int }
  }
  -#[cfg(target_arch = "x86_64")]
  -pub fn open(path: *const c_char, oflag: c_int, mode: mode_t) -> c_int {
  - unsafe { syscall!(OPEN, path, oflag, mode) as c_int }
  -}
  -
  -#[cfg(target_arch = "aarch64")]
  pub fn open(path: *const c_char, oflag: c_int, mode: mode_t) -> c_int {
  unsafe { syscall!(OPENAT, AT_FDCWD, path, oflag, mode) as c_int }
  }
  