start partitioning the diagnostics into two classes: those
that are builtin and those that are aren't.  This is a bunch
of API refactoring that will make this possible, but there is
no functionality change yet.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@44473 91177308-0d34-0410-b5e6-96231b3b80d8
11 files changed