[libc++] Refactor the run-buildbot script to make it more modular, and run the benchmarks

As a fly-by fix, unbreak the benchmarks on Apple platforms.

Differential Revision: https://reviews.llvm.org/D90043

GitOrigin-RevId: 2f8dd2687fa0211ef0c8d2faf74c0e003fe59e7a
1 file changed