[clang] Add tests for some CWG issues from 2024-05-31 telecon (#94167)

This patch adds tests for some CWG issues that were discussed at
2024-05-31 telecon. While all of them are tentatively ready at the
moment, I'm expecting them to be moved to DRs without changes. CWG
issues that are expected to have follow-ups are not included in this PR.

I also realized that `cwg28xx.cpp` has been testing without
`-pedantic-errors`. I fixed that. Fortunately, no existing tests had
anything hidden by the lack of this flag.

The following CWG issues are covered:
[CWG2877](https://cplusplus.github.io/CWG/issues/2877.html) "Type-only
lookup for _using-enum-declarator_"
[CWG2882](https://cplusplus.github.io/CWG/issues/2882.html) "Unclear
treatment of conversion to `void`"
[CWG2883](https://cplusplus.github.io/CWG/issues/2883.html) "Definition
of "odr-usable" ignores lambda scopes"
[CWG2885](https://cplusplus.github.io/CWG/issues/2885.html)
"Non-eligible trivial default constructors"
[CWG2886](https://cplusplus.github.io/CWG/issues/2886.html) "Temporaries
and trivial potentially-throwing special member functions"