[clang] [clang] Fix couroutine error for operator new. (PR #215619)

[Alina Sbirlea via cfe-commits]

alinas wrote:

I'm unsure if this specific change is the (only) one that needs the release notes added, vs the revision that did the changes which introduced the error.

Pinging @ojhunt as the author of the original change to follow up here. My goal is to resolve and get to green again, but I don't have enough clang or coroutine familiarity.

https://github.com/llvm/llvm-project/pull/215619