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

[Peng Liu via cfe-commits]

winner245 wrote:

It is a great new feature which allows us to run benchmark tests in the same way we run a normal test. This indeed simplify the benchmark testing process. I wish I had seen this patch earlier, as the old method of building cxx-benchmarks seemed to have just stopped working, which left me confused until I discovered this patch.

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