[C++ PATCH] Allow __ prefix+suffix on C++11 attribute namespaces (PR c++/86288)

[Jakub Jelinek]

On Thu, Oct 18, 2018 at 12:45:00AM +0200, Jakub Jelinek wrote:
> Is a partial backport (just add
>       attr_id = canonicalize_attr_name (attr_id);
> in the else if (attr_ns) case plus the non-__gnu__ lines from the testcase)
> ok for 7/8 release branches where it ICEs?

Small clarification, only needs to go to 8.x, 7.x compiled it fine, it
got broken with r250911.

	Jakub