[RFE] Support OpenBSD 'CP_SPIN' CPU state in some way

[siebenmann]

In 2018, OpenBSD introduced a new (system) CPU state, CP_SPIN, that counts time the system is stuck spinning on a lock: https://marc.info/?l=openbsd-cvs&m=152630109526317&w=2

The node exporter currently doesn't know about this state, which means that on relevant OpenBSD versions its node_cpu_seconds_total figures are incomplete and break various assumptions that people using them may have (for example, that the total of everything for a single CPU sums to more or less 1). If you want to limit to building on only the currently supported OpenBSD versions, this is straightforward, since both of them should have CP_SPIN and collector/cpu_openbsd.go can just use it.

(I would be happy to prepare a pull request with this small change.)

[discordianfish]

@siebenmann Interesting! Yeah happy to review you PR!

[siebenmann]

The current state is that OpenBSD AMD64 now supports SPIN since commit f8609ae. Other architectures are still lacking support, but that will probably be resolved when pull #1971 lands.

[rexagod]

Hmm, I think this can be closed now.