[llvm] [libc++] Add a workflow to run libc++ benchmarks on historical commits (PR #208080)

[Louis Dionne via llvm-commits]

ldionne wrote:

@boomanaiden154 Do you have thoughts on this? This would allow us to start tracking performance on a regular basis and also generate historical perf data to catch previously-introduced regressions!

https://github.com/llvm/llvm-project/pull/208080