Regression test for the --serialize-diagnostics problem fixed in r221884.



git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@221885 91177308-0d34-0410-b5e6-96231b3b80d8
Remove some redundant virtual on overridden functions

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@222027 91177308-0d34-0410-b5e6-96231b3b80d8