[gardening] Add a helper to SILFunctionConventions to retrieve if a function has a noreturn result.
[gardening] Add a helper to SILFunctionConventions to retrieve if a function has a noreturn result.

Sometimes one just has a SILFunctionConvention instead of the underlying
SILFunctionType (that the SILFunctionConvention contains). This just shims in
that API onto the composition type.

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