[clang] [clang] Allow delayed function instantiation at TU end if initial instantiation fails (PR #117167)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

I am not particularly comfortable/knowledgable in how this all works, but I don't see a problem here.

My current concern is that we're going to get the same error 2x for the same failed instantiation, and that seems unfortunate.

Also, we need a release note.

https://github.com/llvm/llvm-project/pull/117167