Backport change from trunk:
common/debuglog.h: Suppress unused typedef warnings from debugging
logging macros, which occur in functions which always exit via
throwing an exception.

git-svn-id: file:///home/xapian-svn/xapian/branches/1.2@18273 6b2f1b92-a4f3-0310-943f-de3cbe41748b