why is some output placed under "srctree" even if i specify output dir?

[Holger Schurig]

Oh, that's interesting. Because sphinx-build can only be taught about
one sourcedir. But in the srctree != objtree case we have two source
dirs: the in srctree/Documentation with the provided *.rst files, and
the objtree/Documentation/commands, with those files that

   @$(srctree)/Documentation/gen_commands.py $(srctree)
$(objtree)/Documentation/commands

could generate.

Maybe gen_commands should also update the static *.rst files if
srctree != objtree?