Basically a regression after r316268.
However the diagnostic is correct, but the test coverage is bad.

So just like rL316500, introduce yet more tests,
and adjust the release notes.

See https://bugs.llvm.org/show_bug.cgi?id=35200

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@317421 91177308-0d34-0410-b5e6-96231b3b80d8