[llvm] [Support] Add cgroup-aware thread pool strategies (PR #218478)

[Matthias Braun via llvm-commits]

MatzeB wrote:

yeah same question as Arthur, if this is really the recommended form to deal with modern cgroups (I hope there was enough research that this is really the recommended / preferred API to query desired parallelism seems quite complex...) then we may consider using it everywhere in LLVM by default where we could currently go for `sched_getaffinity`...

https://github.com/llvm/llvm-project/pull/218478