[clang] Reland: [clang] unified CWG2398 and P0522 changes; finishes implementation of P3310 (PR #124137)

[Erich Keane via cfe-commits]

erichkeane wrote:

> > Can you explain the revert-issue, and what you did to fix it? The github diff is making REALLY difficult to understand what you did..
> 
> If you go on the commit list, you can click on the commit which I pointed out in the OP ([clang] Changes to template argument list checking", which contains the changes which fix the revert-causing issue)
> 
> The commit message there has explanation of the fix.

Ah, neat.  Github helpfully hid the commit message there for me.  


https://github.com/llvm/llvm-project/pull/124137