named warnings & individual warning control

[DJ Delorie]

> and there should be an unrecognized-warnings warning

I mentioned in a previous post that, rather than remove messages from
the catalog, simply tag them as "obsolete".  That way gcc can detect
that case and warn you.  Without a central database, it's nontrivial
to keep track of obsolete warnings.

> (off by default)

Agreed, especially if you want to silently support multiple versions
of gcc.