tests: re-enable Interpreter/SDK/objc_cast.swift
tests: re-enable Interpreter/SDK/objc_cast.swift

Needed to add some explicit casts to NSObject

rdar://33021520

apple/swift,benlangmuir/swift,benlangmuir/swift,JGiola/swift,parkera/swift,roambotics/swift,glessard/swift,apple/swift,xwu/swift,rudkx/swift,xwu/swift,benlangmuir/swift,JGiola/swift,hooman/swift,hooman/swift,tkremenek/swift,apple/swift,ahoppen/swift,roambotics/swift,JGiola/swift,atrick/swift,JGiola/swift,tkremenek/swift,hooman/swift,rudkx/swift,atrick/swift,ahoppen/swift,tkremenek/swift,xwu/swift,glessard/swift,rudkx/swift,roambotics/swift,apple/swift,hooman/swift,rudkx/swift,apple/swift,parkera/swift,ahoppen/swift,rudkx/swift,xwu/swift,glessard/swift,xwu/swift,tkremenek/swift,JGiola/swift,roambotics/swift,glessard/swift,xwu/swift,parkera/swift,ahoppen/swift,JGiola/swift,apple/swift,tkremenek/swift,roambotics/swift,gregomni/swift,hooman/swift,gregomni/swift,parkera/swift,atrick/swift,parkera/swift,gregomni/swift,rudkx/swift,glessard/swift,parkera/swift,atrick/swift,parkera/swift,gregomni/swift,hooman/swift,benlangmuir/swift,parkera/swift,roambotics/swift,xwu/swift,glessard/swift,tkremenek/swift,gregomni/swift,ahoppen/swift,benlangmuir/swift,atrick/swift,benlangmuir/swift,tkremenek/swift,hooman/swift,gregomni/swift,atrick/swift,ahoppen/swift