gh-101100: Fix broken xrefs in fcntl module doc

[smontanaro]

A few changes:

1. Links for fcntl, ioctl and flock system calls are suppressed. Sphinx only complained about some, but even if it catalogued these somehow, it would likely have been incorrect.
2. Suppress all :const:LOCK_* refs. They appear nowhere else in the Python docs. Users should read the relevant Unix manpages.
3. Convert EACCES an EAGAIN constant references to data references in the errno module.

I'm inclined to move the rather large set of :versionchanged: directives down near the bottom of the file, though for now I left them alone. Almost all of them just identify additions to the set of command constants, and are both platform- and Linux kernel-dependent. As such, they are probably going to be used infrequently. They aren't key to understanding how to use the module.

• Issue: Fix all Sphinx reference warnings in the documentation #101100

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