MS ABI: Mangle this qualifiers on function types

C++11 allows this qualifiers to exist on function types when used in
template arguments.  Previously, I believed it wasn't possible because
MSVC rejected declarations like: S<int () const &> s;

However, it turns out MSVC properly allows them in using declarations;
updated clang to be compatible with this mangling.

llvm-svn: 215464