[-cxx-abi microsoft] Mangle TemplateArgument::Declaration for references

Summary:
Properly mangle declarations showing up in template arguments that are
reference parameters.  Fun-fact: undname cannot handle these!

Reviewers: rnk, cdavis5x

Reviewed By: rnk

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1356