gcc extension documentation?

[Brendan Miller]

Often I want to see what extensions that GCC supports for C++. Some of
this stuff is in the manual, but more often than not I end up finding
docs on third party web sites, or on mailing lists. I'm wondering
where the official docs are?

For example:
__FUNCTION__
__PRETTY_FUNCTION__

are useful GCC specific variables for C++, but I can't seem to find
them documented in the manual. I only see them documented here:

http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/gcc/function-names.html

and mentioned on a few mailist lists.

Is there some place that really lists everything?

Thanks,
Brendan