[Statement checker] Factor out 'fallthrough' checking a bit more.
[Statement checker] Factor out 'fallthrough' checking a bit more.

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