Add a comment and a test to ~DiagnosticEngine about the ordering
requirements on the teardown of DiagnosticConsumer. This could also be
accomplished by rearranging the fields of ~DiagnosticEngine, but I felt
that this was a better, more explicit solution.
This fixes PR21911, an issue that occurred after the unique_ptr
migration in r222193.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@224454 91177308-0d34-0410-b5e6-96231b3b80d8
Reid Kleckner