[PCH] The diagnostic state points can refer to previously created
diagnostic states; make sure the ASTReader sets the diagnostic state
properly instead of always recreating it.

Fixes rdar://12581618 & http://llvm.org/PR14181

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@166987 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed