[PATCH] Add two helper functions: isAtLeastAcquire, isAtLeastRelease

[JF Bastien]

>>! In D4844#5, @morisset wrote:
> If they were for generic instructions, yes (but generic instructions don't have a MemoryOrdering).
> Here they are for loads/stores, which cannot have the acq_rel memory ordering (as said in a comment a few lines before each of my changes).
> If this patch is later extended to RMW instructions, then yes acq_rel will have to be taken into account.

Oh right. Could you add a short comment in each function body?

http://reviews.llvm.org/D4844