Revert "Remove unused variable."

This reverts commit r194485.

The variable is unused in some macro instantiations, but not others. We should
probably fix clang to not warn on this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194486 91177308-0d34-0410-b5e6-96231b3b80d8