atomicops.h on VS2015

[mintyc]

I notice that atomicops.h implements atomic_*_fence on all _MSC_VER

Is there any benefit to make this conditional on say _MSC_VER < 1900 as I think its all present and correct in <atomic> for VS2015

[cameron314]

Probably a good idea. It might take a little while before I get around to it, though.

[mintyc]

I made the change but no significant difference to benchmark numbers (MSVS 2015 CTP 5)

Incidentally profile guided optimisation improves the folly scores by 10% but rest are unaffected

[cameron314]

Interesting, I never thought to try PGO.

I've committed the change (along with a blocking version of the queue) that uses the std:: fences on VS2012+. Thanks for opening this issue!