[clang] [CGExprConstant] stop calling into ConstExprEmitter for Reference type destinations (PR #70366)

[Nick Desaulniers via cfe-commits]

nickdesaulniers wrote:

> I think I'd prefer to avoid calling into ConstExprEmitter at all for cases involving reference binding. I think we've sort of discussed this before. Maybe add a check to tryEmitPrivate()? (We already have a check in tryEmitPrivateForVarInit().)

Done in https://github.com/llvm/llvm-project/pull/70366/commits/4cff8f0f1cb4bba84f32d3953a5abfafd13c6b09 PTAL @efriedma-quic 

https://github.com/llvm/llvm-project/pull/70366