[clang] [clang][C23] N3006 Underspecified object declarations (PR #79845)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

@to268 and I spoke about this offline and we decided to close this PR because it's heading in the wrong direction. We discussed a different direction that focuses solely on implementing the logic to handle `%select{declaration using a deduced type|constexpr declaration}0 %1 also declares %2 which is not an ordinary identifier` as the initial steps towards full support.

https://github.com/llvm/llvm-project/pull/79845