[clang] [clang] Fixed inconsistent diagnostics when initializing a constexpr variable with a compound literal (PR #232825)

[Abdulmalek Almkainzi via cfe-commits]

aalmkainzi wrote:

the problem is compound literal is its own object. so it evals itself and doesn't consider where it is (other than file scope)...

I think my initial solution is ok? The constexpr evaluator checks it later.

https://github.com/llvm/llvm-project/pull/232825