[SSADestroyHoisting] Extracted classifying insts.
[SSADestroyHoisting] Extracted classifying insts.

Extract code for classifying instructions out of the one data flow where
it is currently used into the DeinitBarriers type.  This will facilitate
a second data flow which needs to access the same info and adding an
isBarrier member function to DeinitBarriers for use by folding.

atrick/swift,ahoppen/swift,gregomni/swift,gregomni/swift,rudkx/swift,JGiola/swift,JGiola/swift,roambotics/swift,roambotics/swift,roambotics/swift,gregomni/swift,rudkx/swift,gregomni/swift,apple/swift,roambotics/swift,benlangmuir/swift,benlangmuir/swift,glessard/swift,JGiola/swift,gregomni/swift,atrick/swift,apple/swift,benlangmuir/swift,ahoppen/swift,rudkx/swift,atrick/swift,ahoppen/swift,glessard/swift,JGiola/swift,ahoppen/swift,rudkx/swift,apple/swift,atrick/swift,ahoppen/swift,glessard/swift,ahoppen/swift,apple/swift,rudkx/swift,benlangmuir/swift,JGiola/swift,benlangmuir/swift,roambotics/swift,glessard/swift,glessard/swift,roambotics/swift,benlangmuir/swift,gregomni/swift,atrick/swift,atrick/swift,glessard/swift,apple/swift,apple/swift,JGiola/swift,rudkx/swift