Add support for polymorphic matchers. Use runtime type checking to determine the right polymorphic overload to use.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184558 91177308-0d34-0410-b5e6-96231b3b80d8
Add basic fixit test to template instantiation bug fix (r184503)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184559 91177308-0d34-0410-b5e6-96231b3b80d8