Refactor DelayedDiagnostics so that it keeps diagnostics in
separate pools owned by the RAII objects that keep pushing
decl state.  This gives us quite a bit more flexibility.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@156289 91177308-0d34-0410-b5e6-96231b3b80d8
10 files changed