[ms-cxxabi] Don't consider function templates for name backrefs

They don't seem to be used for back references, presumably because a
function template is unlikely to reoccur, while a class template name
may reoccur as a type.

This fixes a mangling issue for llvm::hash_combine() in Hashing.h.

Reviewers: timurrrr

Differential Revision: http://llvm-reviews.chandlerc.com/D1078