[clang] [clang] Fix crash parsing delayed lambda default arguments (PR #213556)

[Shengxin Pei via cfe-commits]

TPPPP72 wrote:

https://godbolt.org/z/jfojzs8vs

So, clearly, we need to ensure that the function obtained by such code is the lambda's `operator()`.

https://github.com/llvm/llvm-project/pull/213556