documentation: Makefile: turn warnings into errors by default
-W is for turning warnings into errors, --keep-going to make sure the
whole documentation is built and all warnings will be printed before
failing.
Since there's currently no warning, it's time to introduce it!
(From yocto-docs rev: 5d7b8547549b2203a03df617cdba70ccf2194c62)
Signed-off-by: Quentin Schulz <foss@0leil.net>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Quentin Schulz