HEADS UP: As of r233419, head should compile cleanly with clang

Hi,

As of r233419 in head, you should now be able to build world and the
GENERIC kernel using clang, and without the need to place NO_WERROR=
and/or WERROR= in your src.conf file.

Note this is only valid for i386 and amd64, and there are still some
non-standard world settings that lead to warnings that break the build.
For example, WITH_ICONV does not fully work yet.

Also, not all kernel configurations will fully compile without warnings.
If there are any clang-specific warnings that you get for your custom
kernel configuration, please let me know, so I can go hunting for a
proper fix or workaround.

Last but not least, it would be nice to have world and kernel not
regress anymore, so if there is somebody who can offer resources for a
tinderbox or other continuous head build with clang, please speak up. :)