msgpack: remove -Werror from subdirectories

[l29ah]

You should've squashed your commits, but okay.

-- () ascii ribbon campaign - against html mail /\ http://arc.pasp.de/ - against proprietary attachments

[chrboe]

fyi, there's a squash option when merging a PR: https://help.github.com/articles/about-pull-request-merges/

you're welcome