Implement the suggested resolution to core issue 547, extended to also

Implement the suggested resolution to core issue 547, extended to also
allow ref-qualifiers on function types used as template type
arguments. GNU actually allows cv-qualifiers on function types in many
places where it shouldn't, so we currently categorize this as a GNU
extension.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@124584 91177308-0d34-0410-b5e6-96231b3b80d8