[Bugfix] fix r369705 unit test

Summary:
Aliases aren't supported on OSX.  Add a GNU target triple.

Reported-by: leonardchan
Reported-by: erik.pilkington

Reviewers: leonardchan, erik.pilkington

Reviewed By: leonardchan, erik.pilkington

Subscribers: dexonsmith, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66622

llvm-svn: 369713