named warnings & individual warning control

[DJ Delorie]

> And the strings would be fixed for a given instantiation of the
> compiler,

Assuming you're able to scan all the possible target backends and
language frontends, yes.  Relying on that automatically precludes
third parties adding their own targets or languages without figuring
out how to reliably regenerate the hash.

I suspect a more general purpose hash would be easier to manage.