[clang] [libcxx] [Clang] Add __builtin_invoke and use it in libc++ (PR #116709)

[Nikolas Klauser via cfe-commits]

philnik777 wrote:

@alexfh Could you maybe provide a reproducer without a dependency on Google Test? I don't easily have access to that, and it shouldn't be too hard to remove that. It looks to me like it's instantiating the variant constructor with something, but unfortunately the diagnostics are cut off at exactly that point.

https://github.com/llvm/llvm-project/pull/116709