header. This showed up in client code that has a different include
ordering after Chris's shuffle of raw_ostream. All of the Clang code
ends up with a header included before this one that provides the needed
type and using declaration.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@135765 91177308-0d34-0410-b5e6-96231b3b80d8