[Polly] Clang complains about missing virtual destructor

Summary: Feel free to reassign if needed.

Reviewers: mhalk, bollu, jdoerfert

Reviewed By: jdoerfert

Subscribers: jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64786

llvm-svn: 366697