[libcxx] [llvm] [libc++] Unify the benchmarks with the test suite (PR #101399)

[Nikolas Klauser via llvm-commits]

https://github.com/philnik777 commented:

I really like this. Not having to figure out how to build and run the benchmarks every time would be quite nice. It's also quite nice to be able to run the benchmarks in different configurations more easily.

https://github.com/llvm/llvm-project/pull/101399