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

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman requested changes to this pull request.

Precommit CI failures look related to this patch:
```
/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-g6cdk-1/llvm-project/github-pull-requests/build-runtimes/include/c++/v1/__type_traits/invoke.h:123:29: error: variable has incomplete type 'struct _LIBCPP_TEMPLATE_VIS'
  123 | struct _LIBCPP_TEMPLATE_VIS is_invocable : bool_constant<__is_invocable_v<_Fn, _Args...> > {};
      |                             ^
```

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