[Bug c/89051] -Wno-error= does not work for warning groups

[m101010a at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89051

--- Comment #2 from m101010a at gmail dot com ---
(In reply to Martin Sebor from comment #1)
> I don't think GCC has an internal representation of warning groups

It has to have some representation, because it can tell which warning group is
more specific (the documentation specifically mentions this, and it works in
practice).  That representation might be able to be re-used to mark which
groups are also errors.