[clang] [C++20][Coroutines] Lambda-coroutine with operator new in promise_type (PR #84193)

[Yanzuo Liu via cfe-commits]

zwuis wrote:

Hi. I tried to fix this issue locally by adding a function `__builtin_lambda_this()` and it seems to work. I can create PR if you think this is a good approach. And I have some questions:

1. Should this builtin function handle lambda expression only? What about `__builtin_member_function_caller()`?
2. Is RFC needed to add this builtin function?
3. How to handle non-static captureless lambda expression? Following current resolution of [CWG3040](https://cplusplus.github.io/CWG/issues/3040.html)?

https://github.com/llvm/llvm-project/pull/84193