[3.9] gh-97897: Prevent os.mkfifo and os.mknod segfaults with macOS 13 SDK (GH-97944) (#97968)

The macOS 13 SDK includes support for the `mkfifoat` and `mknodat` system calls.
 Using the `dir_fd` option with either `os.mkfifo` or `os.mknod` could result in a
 segfault if cpython is built with the macOS 13 SDK but run on an earlier
 version of macOS. Prevent this by adding runtime support for detection of
 these system calls ("weaklinking") as is done for other newer syscalls on
 macOS.
(cherry picked from commit 6d0a0191)

Co-authored-by: Ned Deily <nad@python.org>