Fix PR21684 - Ellipsis following an 'auto' parameter sans name/ID 
should indicate a c++ parameter pack not a c-variadic.

int i = [](auto...) { return 0; }(); // OK now.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@223357 91177308-0d34-0410-b5e6-96231b3b80d8