Needs pause intrinsic/wrapper in druntime, but where?

[Manu]

I need a pause() function in druntime (wrap x86 `pause`/arm `yield`,
etc), but it's not clear where to put it...
Candidates are:
  core.atomic - seems odd, but it's almost exclusively used when
implementing spin locks
  core.thread - sounds appropriate, but doesn't really mean anything wrt threads
  core.sync.??? - no appropriate sub-package appears to exist...

Ideas?
I'm leaning towards core.atomic.