The Great -Wundef purge - Read this if you have a -Wundef-fix patch!

[Carlos O'Donell]

Community,

We are only just starting to formulate some best practice
for cleaning up the -Wundef warnigs. I appreciate the patience
everyone has had in these discussions.

I've taken what we've been talking about and distilled them into
this document:

https://sourceware.org/glibc/wiki/Wundef

All developers working on fixing -Wundef warnings should have a
look at this document and if anything seems wrong please comment.

Cheers,
Carlos.