tools/docs/sphinx-build-wrapper: Emit $SPHINXOPTS later in args list

tools/docs/sphinx-build-wrapper: Emit $SPHINXOPTS later in args list

The option list to sphinx-build via SPHINXOPTS should have higher
priority than those the wrapper comes up with.
sphinx-build will choose the latest one if there are duplicates.

To restore the behavior of Makefile era, when the documentation builds
at https://www.kernel.org/doc/html/next/ had been depending on it,
reorder the flag list.

Reported-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
Closes: https://lore.kernel.org/20251007-awesome-guan-of-greatness-e6ec75@lemur/
Reported-by: Akira Yokosawa <akiyks@gmail.com>
Closes: https://lore.kernel.org/c35e690f-0579-49cb-850c-07af98e5253a@gmail.com/
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <eaf4bfd8-fb80-45d0-b3ec-4047692ebbed@gmail.com>