Fix PR 33189: Clang assertion on template destructor declaration

Summary:
This patch aims to fix the bug reported at
https://bugs.llvm.org/show_bug.cgi?id=33189. Clang hits an assertion
when a template destructor declaration is present. This is caused by
later processing that does not expect to encounter a template when
looking at a destructor. The resolution is to treat the destructor as
being not declared when later processing is interested in the properties
of the destructor of a class.

Reviewers: rcraik, hubert.reinterpretcast, aaron.ballman, rsmith

Reviewed By: rsmith

Subscribers: rsmith, cfe-commits

Differential Revision: https://reviews.llvm.org/D33833

Patch by Kuang He!

llvm-svn: 306905