Try to recover a bit better if a close brace is missing from the end of a class

Try to recover a bit better if a close brace is missing from the end of a class
definition. If we see something that looks like a namespace definition inside a
class, that strongly indicates that a close brace was missing somewhere.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194319 91177308-0d34-0410-b5e6-96231b3b80d8