Fix build warnings introduced in rL347938

Summary:
Suppressed warnings in release builds due to variable used
only in assert statement.

Subscribers: llvm-commits, eraman, mgorny

Differential Revision: https://reviews.llvm.org/D55100

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@347939 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed