[libclang] Visit attributes for function and class templates
Summary: Previously, VisitAttributes was not called for function and class templates and thus their attributes were not accessible using libclang.
Reviewers: bkramer, arphaman, rsmith, jbcoe
Reviewed By: jbcoe
Patch by jklaehn (Johann Klähn)
Differential Revision: https://reviews.llvm.org/D36955