clang and bdb

In case anyone else runs into this clang and bdb don't get along. Seeing as
we're somewhat stuck in the past now that bdb's licensing has changed, it's
unlikely that this will be fixed in newer versions.

Specifically clang fails because bdb reimplements builtins.

This post on the FreeBSD list has the details and a patch:
http://lists.freebsd.org/pipermail/freebsd-current/2012-May/033615.html

I've attached the patch to this email since the version that's on that mail is
a patch against the packaging system at FreeBSD.