Updated a usage of createTemporaryFile that does not expect file to be created.

Summary:
This fixes a usage of createTemporaryFile in clang repo after
a change in llvm repo.

Reviewers: klimek, bkramer, krasimir, espindola, ilya-biryukov

Reviewed By: ilya-biryukov

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D36828

llvm-svn: 327852