remove warnings from google-benchmarks in libcxx

Differential Revision: https://reviews.llvm.org/D25522

Patch written by Aditya Kumar.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@284179 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed