[clang] [Clang] Skip past code generation for unevaluated lambdas (PR #124572)

[via cfe-commits]

cor3ntin wrote:

@efriedma-quic So we would track that a function that was declared in an unevaluated context has "unevaluated linkage" (or really, a bit that said it was declared in unevaluated context), and skip them in `EmitTopLevelDecl` like we do for immediate functions?

Seems reasonable (and I prefer that to inventing mangling, in think)

https://github.com/llvm/llvm-project/pull/124572