[ms-cxxabi] Mangle function pointer template arguments correctly

Reviewers: rjmccall

CC: timurrrr, llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D554

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177589 91177308-0d34-0410-b5e6-96231b3b80d8