[clang] No longer add enumeration constants to the wrong scope (PR #134998)

[Richard Smith via cfe-commits]

zygoloid wrote:

> > I thought CWG's preferred direction on this was to reject entirely?
> 
> What do they wish to reject? Defining an enum in a different declaration context than its primary context? That seems odd.
> 
> Do you have an idea of the CWG DR? We looked but couldn't find anything that looked like it.

[CWG1485](https://cplusplus.github.io/CWG/issues/1485.html): "CWG agreed that an unscoped opaque enumeration in class scope should be forbidden."

https://github.com/llvm/llvm-project/pull/134998