[clang] [OpenACC] Improve C++20 compatibility of private/firstprivate test (PR #152233)

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.

Ah, hrmph, I hadn't thought of this, thanks for bringing it up!  

Instead of the macro/etc, can you just do these unconditionally (plus remove the aggregate/value init?)?  Those two are irrelevant for the diagnostics being looked for in both modes, so just `DeletedCopy();`(or defaulted, etc) and `DefaultedCopy();` are more than OK.  I'd rather not have the rest.

In short, remove the ifdef + comment, and this is LGTM.

<side note: If you don't update this within the next ~6 hours, I will be away for a week, so I'll approve this contingent on the above so this doesnt have to wait>

https://github.com/llvm/llvm-project/pull/152233