The sphinx support is fairly new and we don't seem to have all the
bugs worked out for cross development environments right now.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200203090932.19147-6-alex.bennee@linaro.org>