Prevent Sphinx 4 and later from creating subdirectories, which
the build scripts are not equipped to deal with.

Taken from upstream:
https://gitlab.com/qemu-project/qemu/-/issues/256
https://gitlab.com/qemu-project/qemu/-/commit/269a7e97865cb863c9ca19e5f2e6a40ac9eddf82

diff --git a/docs/conf.py b/docs/conf.py
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -279,6 +279,7 @@
      ['Stefan Hajnoczi <stefanha@redhat.com>',
       'Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>'], 1),
 ]
+man_make_section_directory = False
 
 # -- Options for Texinfo output -------------------------------------------