configure.ac: add -Werror to default compiler options

[Per Johansson]

(resent with correct from-address, please ignore the previous one)

1 sep 2011 kl. 03:27 skrev Dan Kegel:

> At which point it would probably be a fine idea to add -Werror by default;
> buildbot will help keep everyone in sync, even if they're using a compiler
> that doesn't catch as many warnings as the one buildbot uses.

We use -Werror at my company, but I think you should really think twice before enabling it for a distributed package. New compiler versions add new warnings. Usually correctly so, but there's no way to know what warnings will be produced by what compiler, and keeping up with new compilers requires a bit of effort. We make sure to always test new compilers separately before upgrading on the developing machines.

I think most users will probably just see that the package fails to build, and assume it's broken.

Ps. I know there's also a few warnings while building on OS X. I don't have access to it now, or I'd send the list.
-- 
Per Johansson