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

[Yanzuo Liu via cfe-commits]

zwuis wrote:

> Then what is the benefits?

Adding `__builtin_lambda_this()` is prerequisite of fixing the issue which this PR tries to fix, because we cannot access the caller of lambda `operator()` without adding compiler magic such as builtin functions.

> Whatever it is, I feel this can/should be a RFC. Since it is relate to the fundamental design of AST.

Get it. Thanks!

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