Although I don't plan to bring over new assertions wholesale
into the current qualification branch, it's entirely possible
that various minor changes in main will use the new assertions;
having this basic support in the release branch will simplify that.
(This is why I'm adding the includes as a separate pass from
rewriting the individual assertions)
This simplifies fixing the master-next build. Upstream LLVM already
has a copy of this function, so on master-next we only need to delete
the Swift copy, reducing the potential for merge conflicts.
