cpuset: Add a -g mode to print the number of CPUs in the set

[markj]

Summary

Just a proposal, no man page update yet.

[markj]

Provide a -H flag to suppress printing of headers.

[mjg]

I don't think splitting this into 2 printf statements buys anything, but functionality LGTM

[mjg]

can this go in please?

[mjg]

As I said few times this is blockign some other stuff, most notably passing a small thread limit to the llvm linker.

if this or something else providing this functinality does not land till friday next week I'm going to commit my original patch from D36351

[mjg]

i'm going to commit some time over the weekend