[TypeChecker] [NFC] Make unreachable case unreachable
[TypeChecker] [NFC] Make unreachable case unreachable

A part of swift::diagnoseExplicitUnavailability() that should never run for deprecations looks for them and handles them with “break”. Change this to llvm_unreachable() so we notice if this somehow happens.

This change *should* be NFC; I’m splitting it out from other changes so that bisections can point to it if it causes problems in the future.

jmgc/swift,parkera/swift,sschiau/swift,rudkx/swift,sschiau/swift,allevato/swift,tkremenek/swift,ahoppen/swift,devincoughlin/swift,sschiau/swift,sschiau/swift,tkremenek/swift,nathawes/swift,devincoughlin/swift,sschiau/swift,karwa/swift,aschwaighofer/swift,tkremenek/swift,allevato/swift,JGiola/swift,xwu/swift,hooman/swift,jmgc/swift,karwa/swift,shajrawi/swift,shahmishal/swift,xedin/swift,glessard/swift,airspeedswift/swift,shajrawi/swift,xwu/swift,CodaFi/swift,atrick/swift,lorentey/swift,aschwaighofer/swift,glessard/swift,xedin/swift,devincoughlin/swift,JGiola/swift,stephentyrone/swift,hooman/swift,nathawes/swift,CodaFi/swift,gribozavr/swift,karwa/swift,karwa/swift,shajrawi/swift,JGiola/swift,aschwaighofer/swift,gregomni/swift,stephentyrone/swift,shahmishal/swift,stephentyrone/swift,shahmishal/swift,hooman/swift,nathawes/swift,benlangmuir/swift,shajrawi/swift,roambotics/swift,apple/swift,nathawes/swift,shajrawi/swift,hooman/swift,devincoughlin/swift,xwu/swift,gregomni/swift,lorentey/swift,stephentyrone/swift,devincoughlin/swift,ahoppen/swift,sschiau/swift,roambotics/swift,benlangmuir/swift,xwu/swift,jckarter/swift,allevato/swift,parkera/swift,harlanhaskins/swift,gribozavr/swift,airspeedswift/swift,shahmishal/swift,jmgc/swift,jckarter/swift,CodaFi/swift,stephentyrone/swift,xwu/swift,apple/swift,gribozavr/swift,karwa/swift,allevato/swift,rudkx/swift,nathawes/swift,xedin/swift,ahoppen/swift,gregomni/swift,JGiola/swift,aschwaighofer/swift,rudkx/swift,karwa/swift,JGiola/swift,lorentey/swift,benlangmuir/swift,harlanhaskins/swift,gribozavr/swift,shahmishal/swift,tkremenek/swift,aschwaighofer/swift,lorentey/swift,roambotics/swift,aschwaighofer/swift,devincoughlin/swift,nathawes/swift,airspeedswift/swift,stephentyrone/swift,jckarter/swift,xedin/swift,atrick/swift,sschiau/swift,hooman/swift,airspeedswift/swift,shahmishal/swift,rudkx/swift,benlangmuir/swift,xedin/swift,devincoughlin/swift,shajrawi/swift,atrick/swift,jckarter/swift,apple/swift,hooman/swift,allevato/swift,jmgc/swift,lorentey/swift,gribozavr/swift,apple/swift,jckarter/swift,allevato/swift,roambotics/swift,apple/swift,ahoppen/swift,gregomni/swift,glessard/swift,lorentey/swift,xedin/swift,rudkx/swift,harlanhaskins/swift,shahmishal/swift,harlanhaskins/swift,glessard/swift,jmgc/swift,atrick/swift,apple/swift,CodaFi/swift,benlangmuir/swift,karwa/swift,xedin/swift,jckarter/swift,allevato/swift,harlanhaskins/swift,ahoppen/swift,glessard/swift,parkera/swift,parkera/swift,xedin/swift,CodaFi/swift,CodaFi/swift,ahoppen/swift,rudkx/swift,CodaFi/swift,parkera/swift,harlanhaskins/swift,lorentey/swift,lorentey/swift,roambotics/swift,tkremenek/swift,jmgc/swift,parkera/swift,airspeedswift/swift,jmgc/swift,JGiola/swift,roambotics/swift,aschwaighofer/swift,tkremenek/swift,karwa/swift,jckarter/swift,sschiau/swift,parkera/swift,hooman/swift,atrick/swift,tkremenek/swift,shahmishal/swift,airspeedswift/swift,gribozavr/swift,devincoughlin/swift,benlangmuir/swift,glessard/swift,gregomni/swift,atrick/swift,shajrawi/swift,stephentyrone/swift,shajrawi/swift,nathawes/swift,airspeedswift/swift,parkera/swift,gregomni/swift,xwu/swift,harlanhaskins/swift,gribozavr/swift,gribozavr/swift,xwu/swift