Code review comment for lp://qastaging/~alan-griffiths/mir/keep-helgrind-happy

I feel static is a hack (but is a solution too). Also, this proposal doesn't silence the races reported for std::atomic.

I've made a separate proposal that fixes all the races, for helgrind cleanliness:
https://code.launchpad.net/~vanvugt/mir/fix-1282886/+merge/207596