[Test] Don't test _swift_willThrow on older runtimes.
[Test] Don't test _swift_willThrow on older runtimes.

rdar://problem/56752866
parkera/swift,aschwaighofer/swift,benlangmuir/swift,harlanhaskins/swift,tkremenek/swift,gribozavr/swift,allevato/swift,gregomni/swift,atrick/swift,allevato/swift,gregomni/swift,parkera/swift,harlanhaskins/swift,gregomni/swift,nathawes/swift,benlangmuir/swift,JGiola/swift,jmgc/swift,harlanhaskins/swift,CodaFi/swift,apple/swift,parkera/swift,ahoppen/swift,benlangmuir/swift,glessard/swift,hooman/swift,nathawes/swift,hooman/swift,airspeedswift/swift,gribozavr/swift,CodaFi/swift,karwa/swift,ahoppen/swift,xwu/swift,atrick/swift,karwa/swift,lorentey/swift,aschwaighofer/swift,roambotics/swift,gregomni/swift,aschwaighofer/swift,xwu/swift,harlanhaskins/swift,CodaFi/swift,rudkx/swift,gribozavr/swift,allevato/swift,tkremenek/swift,jmgc/swift,CodaFi/swift,atrick/swift,JGiola/swift,jmgc/swift,lorentey/swift,jckarter/swift,parkera/swift,jmgc/swift,aschwaighofer/swift,roambotics/swift,stephentyrone/swift,gregomni/swift,nathawes/swift,jckarter/swift,karwa/swift,xwu/swift,tkremenek/swift,nathawes/swift,gribozavr/swift,rudkx/swift,xwu/swift,jmgc/swift,nathawes/swift,harlanhaskins/swift,apple/swift,xwu/swift,gribozavr/swift,lorentey/swift,tkremenek/swift,apple/swift,jckarter/swift,airspeedswift/swift,jckarter/swift,stephentyrone/swift,gribozavr/swift,rudkx/swift,aschwaighofer/swift,stephentyrone/swift,gribozavr/swift,karwa/swift,karwa/swift,roambotics/swift,stephentyrone/swift,JGiola/swift,roambotics/swift,roambotics/swift,allevato/swift,stephentyrone/swift,rudkx/swift,parkera/swift,glessard/swift,karwa/swift,stephentyrone/swift,glessard/swift,apple/swift,ahoppen/swift,hooman/swift,benlangmuir/swift,airspeedswift/swift,parkera/swift,JGiola/swift,CodaFi/swift,hooman/swift,hooman/swift,lorentey/swift,roambotics/swift,lorentey/swift,glessard/swift,xwu/swift,lorentey/swift,allevato/swift,JGiola/swift,nathawes/swift,parkera/swift,benlangmuir/swift,karwa/swift,glessard/swift,atrick/swift,nathawes/swift,jmgc/swift,airspeedswift/swift,apple/swift,ahoppen/swift,tkremenek/swift,jckarter/swift,CodaFi/swift,jmgc/swift,airspeedswift/swift,rudkx/swift,hooman/swift,benlangmuir/swift,parkera/swift,allevato/swift,tkremenek/swift,CodaFi/swift,tkremenek/swift,rudkx/swift,harlanhaskins/swift,JGiola/swift,stephentyrone/swift,hooman/swift,xwu/swift,lorentey/swift,karwa/swift,gregomni/swift,aschwaighofer/swift,jckarter/swift,airspeedswift/swift,gribozavr/swift,aschwaighofer/swift,jckarter/swift,ahoppen/swift,allevato/swift,lorentey/swift,harlanhaskins/swift,ahoppen/swift,atrick/swift,apple/swift,airspeedswift/swift,atrick/swift,glessard/swift