I would really like to write the handlers in terms of C++11 atomics. This...

I would really like to write the handlers in terms of C++11 atomics.  This would give us the best performance, portablity, and safety tradeoff.  Unfortunately I can not yet do that.  So I've put the desired code in comments, and reverted the handler getters to the slower but safer legacy atomic intrinsics.

llvm-svn: 153041