[clang] [Clang] Follow up to previous lambda-in-concept patch (PR #210381)

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.

I think this seems reasonable based on the explaination.  Please give the others a little bit to take a look at this before merging.

https://github.com/llvm/llvm-project/pull/210381