Fix test/IRGen/objc_generic_class_stub.swift for 32-bit platforms
Fix test/IRGen/objc_generic_class_stub.swift for 32-bit platforms

Fixes <rdar://problem/71476765>.

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