[clang] [Clang] Support using boolean vectors in ternary operators (PR #154145)

[Erich Keane via cfe-commits]

erichkeane wrote:

> errors, but I think to fold it directly we'd need a dedicated builtin. But I'm not a master of the clang AST.

We shouldn't need a builtin, we should just be able to handle the AST nodes directly in ExprConstant.cpp.

https://github.com/llvm/llvm-project/pull/154145