Fix and recommit r339382 based on solution from RSmith:

As sent on cfe-commits:
 "You need to use "friend TrailingObjects;" here, not 
 "friend class TrailingObjects;", to avoid breaking MSVC 
 (which doesn't implement injected-class-names quite according to spec)."


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@339389 91177308-0d34-0410-b5e6-96231b3b80d8