[libc] Fix benchmarks CMakeLists.txt

Summary:
This is a follow up on https://reviews.llvm.org/rGaba80d0734d1#886881.
`target_link_options` requires CMake>=3.13.

Reviewers: abrachet

Subscribers: mgorny, MaskRay, tschuett, libc-commits

Tags: #libc-project

Differential Revision: https://reviews.llvm.org/D73452