IRGen: Don't emit ConstantRefs to empty globals.
IRGen: Don't emit ConstantRefs to empty globals.

We don't emit empty global variables, so we shouldn't emit references to them either.

Swift SVN r4707

ken0nek/swift,OscarSwanros/swift,felix91gr/swift,slavapestov/swift,milseman/swift,danielmartin/swift,LeoShimonaka/swift,bitjammer/swift,harlanhaskins/swift,glessard/swift,russbishop/swift,CodaFi/swift,roambotics/swift,kentya6/swift,slavapestov/swift,cbrentharris/swift,practicalswift/swift,gmilos/swift,parkera/swift,adrfer/swift,jmgc/swift,frootloops/swift,tkremenek/swift,hooman/swift,austinzheng/swift,kperryua/swift,codestergit/swift,Ivacker/swift,cbrentharris/swift,deyton/swift,arvedviehweger/swift,natecook1000/swift,russbishop/swift,johnno1962d/swift,frootloops/swift,gribozavr/swift,brentdax/swift,Jnosh/swift,swiftix/swift,harlanhaskins/swift,jtbandes/swift,karwa/swift,alblue/swift,slavapestov/swift,tardieu/swift,kperryua/swift,mightydeveloper/swift,mightydeveloper/swift,IngmarStein/swift,OscarSwanros/swift,hughbe/swift,alblue/swift,kentya6/swift,Ivacker/swift,tkremenek/swift,deyton/swift,huonw/swift,milseman/swift,Jnosh/swift,huonw/swift,Ivacker/swift,dduan/swift,xedin/swift,natecook1000/swift,aschwaighofer/swift,benlangmuir/swift,danielmartin/swift,tinysun212/swift-windows,LeoShimonaka/swift,karwa/swift,JaSpa/swift,lorentey/swift,stephentyrone/swift,airspeedswift/swift,frootloops/swift,modocache/swift,tardieu/swift,austinzheng/swift,djwbrown/swift,JaSpa/swift,parkera/swift,codestergit/swift,jckarter/swift,KrishMunot/swift,shajrawi/swift,shajrawi/swift,OscarSwanros/swift,harlanhaskins/swift,dduan/swift,airspeedswift/swift,swiftix/swift,natecook1000/swift,swiftix/swift.old,felix91gr/swift,return/swift,CodaFi/swift,CodaFi/swift,devincoughlin/swift,xwu/swift,tkremenek/swift,OscarSwanros/swift,slavapestov/swift,atrick/swift,bitjammer/swift,sschiau/swift,xedin/swift,therealbnut/swift,parkera/swift,Jnosh/swift,parkera/swift,amraboelela/swift,calebd/swift,therealbnut/swift,harlanhaskins/swift,gribozavr/swift,tardieu/swift,manavgabhawala/swift,aschwaighofer/swift,zisko/swift,modocache/swift,gregomni/swift,kusl/swift,uasys/swift,alblue/swift,brentdax/swift,emilstahl/swift,kusl/swift,codestergit/swift,ben-ng/swift,shajrawi/swift,karwa/swift,alblue/swift,bitjammer/swift,kstaring/swift,gregomni/swift,ahoppen/swift,natecook1000/swift,arvedviehweger/swift,lorentey/swift,amraboelela/swift,IngmarStein/swift,kusl/swift,milseman/swift,jmgc/swift,aschwaighofer/swift,allevato/swift,hooman/swift,jopamer/swift,gmilos/swift,karwa/swift,swiftix/swift.old,ken0nek/swift,lorentey/swift,tardieu/swift,shahmishal/swift,manavgabhawala/swift,hughbe/swift,devincoughlin/swift,uasys/swift,xwu/swift,JGiola/swift,SwiftAndroid/swift,gregomni/swift,sdulal/swift,amraboelela/swift,jopamer/swift,hughbe/swift,ahoppen/swift,MukeshKumarS/Swift,therealbnut/swift,swiftix/swift.old,mightydeveloper/swift,stephentyrone/swift,KrishMunot/swift,jckarter/swift,roambotics/swift,russbishop/swift,shajrawi/swift,Jnosh/swift,alblue/swift,sdulal/swift,KrishMunot/swift,tardieu/swift,xwu/swift,deyton/swift,modocache/swift,swiftix/swift.old,modocache/swift,tinysun212/swift-windows,kentya6/swift,calebd/swift,jtbandes/swift,calebd/swift,gottesmm/swift,sdulal/swift,cbrentharris/swift,benlangmuir/swift,kentya6/swift,apple/swift,hooman/swift,gribozavr/swift,JGiola/swift,sdulal/swift,kstaring/swift,djwbrown/swift,nathawes/swift,cbrentharris/swift,LeoShimonaka/swift,kperryua/swift,LeoShimonaka/swift,gribozavr/swift,xedin/swift,jckarter/swift,gribozavr/swift,arvedviehweger/swift,johnno1962d/swift,felix91gr/swift,JaSpa/swift,kusl/swift,allevato/swift,zisko/swift,KrishMunot/swift,modocache/swift,LeoShimonaka/swift,kstaring/swift,return/swift,airspeedswift/swift,shajrawi/swift,shahmishal/swift,CodaFi/swift,codestergit/swift,milseman/swift,MukeshKumarS/Swift,stephentyrone/swift,dduan/swift,gmilos/swift,johnno1962d/swift,modocache/swift,JaSpa/swift,khizkhiz/swift,devincoughlin/swift,rudkx/swift,austinzheng/swift,return/swift,gribozavr/swift,rudkx/swift,jtbandes/swift,JaSpa/swift,natecook1000/swift,milseman/swift,gottesmm/swift,tjw/swift,khizkhiz/swift,karwa/swift,airspeedswift/swift,austinzheng/swift,xedin/swift,gregomni/swift,adrfer/swift,emilstahl/swift,uasys/swift,airspeedswift/swift,jckarter/swift,shahmishal/swift,ben-ng/swift,frootloops/swift,Ivacker/swift,nathawes/swift,slavapestov/swift,emilstahl/swift,IngmarStein/swift,hooman/swift,CodaFi/swift,gribozavr/swift,hooman/swift,bitjammer/swift,JGiola/swift,deyton/swift,therealbnut/swift,kusl/swift,milseman/swift,djwbrown/swift,gmilos/swift,practicalswift/swift,frootloops/swift,jckarter/swift,deyton/swift,manavgabhawala/swift,jtbandes/swift,glessard/swift,calebd/swift,felix91gr/swift,allevato/swift,allevato/swift,CodaFi/swift,bitjammer/swift,lorentey/swift,OscarSwanros/swift,shahmishal/swift,kusl/swift,deyton/swift,cbrentharris/swift,MukeshKumarS/Swift,rudkx/swift,aschwaighofer/swift,ahoppen/swift,Jnosh/swift,alblue/swift,johnno1962d/swift,JGiola/swift,johnno1962d/swift,danielmartin/swift,tjw/swift,kentya6/swift,karwa/swift,manavgabhawala/swift,KrishMunot/swift,austinzheng/swift,calebd/swift,kperryua/swift,ken0nek/swift,LeoShimonaka/swift,hooman/swift,tjw/swift,kperryua/swift,modocache/swift,swiftix/swift,deyton/swift,dduan/swift,SwiftAndroid/swift,johnno1962d/swift,harlanhaskins/swift,russbishop/swift,djwbrown/swift,karwa/swift,ahoppen/swift,IngmarStein/swift,dreamsxin/swift,gottesmm/swift,amraboelela/swift,slavapestov/swift,tkremenek/swift,gregomni/swift,ben-ng/swift,khizkhiz/swift,gottesmm/swift,IngmarStein/swift,ahoppen/swift,xwu/swift,jtbandes/swift,emilstahl/swift,dreamsxin/swift,kperryua/swift,calebd/swift,shahmishal/swift,tinysun212/swift-windows,natecook1000/swift,karwa/swift,gribozavr/swift,allevato/swift,lorentey/swift,sschiau/swift,khizkhiz/swift,SwiftAndroid/swift,apple/swift,glessard/swift,jopamer/swift,ben-ng/swift,gmilos/swift,kentya6/swift,adrfer/swift,zisko/swift,swiftix/swift.old,brentdax/swift,huonw/swift,kstaring/swift,IngmarStein/swift,djwbrown/swift,swiftix/swift.old,Jnosh/swift,bitjammer/swift,danielmartin/swift,allevato/swift,brentdax/swift,sdulal/swift,jmgc/swift,uasys/swift,zisko/swift,xedin/swift,swiftix/swift,allevato/swift,Ivacker/swift,sdulal/swift,nathawes/swift,rudkx/swift,jtbandes/swift,kstaring/swift,lorentey/swift,therealbnut/swift,SwiftAndroid/swift,calebd/swift,apple/swift,codestergit/swift,parkera/swift,gmilos/swift,benlangmuir/swift,return/swift,parkera/swift,djwbrown/swift,benlangmuir/swift,gottesmm/swift,mightydeveloper/swift,roambotics/swift,Ivacker/swift,swiftix/swift.old,arvedviehweger/swift,airspeedswift/swift,ben-ng/swift,aschwaighofer/swift,MukeshKumarS/Swift,jopamer/swift,xedin/swift,glessard/swift,slavapestov/swift,jmgc/swift,shajrawi/swift,glessard/swift,Jnosh/swift,manavgabhawala/swift,zisko/swift,practicalswift/swift,khizkhiz/swift,felix91gr/swift,jmgc/swift,frootloops/swift,ken0nek/swift,lorentey/swift,mightydeveloper/swift,sschiau/swift,khizkhiz/swift,adrfer/swift,tinysun212/swift-windows,kperryua/swift,amraboelela/swift,gregomni/swift,emilstahl/swift,johnno1962d/swift,apple/swift,gmilos/swift,practicalswift/swift,arvedviehweger/swift,nathawes/swift,benlangmuir/swift,danielmartin/swift,tjw/swift,sschiau/swift,uasys/swift,arvedviehweger/swift,rudkx/swift,dduan/swift,huonw/swift,uasys/swift,glessard/swift,nathawes/swift,OscarSwanros/swift,tinysun212/swift-windows,roambotics/swift,xwu/swift,practicalswift/swift,cbrentharris/swift,tardieu/swift,kstaring/swift,manavgabhawala/swift,practicalswift/swift,JaSpa/swift,mightydeveloper/swift,codestergit/swift,swiftix/swift.old,jtbandes/swift,ben-ng/swift,khizkhiz/swift,tjw/swift,SwiftAndroid/swift,jckarter/swift,xwu/swift,alblue/swift,gottesmm/swift,ken0nek/swift,IngmarStein/swift,LeoShimonaka/swift,jopamer/swift,jopamer/swift,MukeshKumarS/Swift,aschwaighofer/swift,adrfer/swift,amraboelela/swift,harlanhaskins/swift,zisko/swift,felix91gr/swift,JGiola/swift,airspeedswift/swift,brentdax/swift,felix91gr/swift,devincoughlin/swift,shajrawi/swift,practicalswift/swift,tkremenek/swift,kentya6/swift,jckarter/swift,jmgc/swift,MukeshKumarS/Swift,austinzheng/swift,Ivacker/swift,roambotics/swift,hughbe/swift,shahmishal/swift,devincoughlin/swift,emilstahl/swift,kentya6/swift,russbishop/swift,devincoughlin/swift,codestergit/swift,brentdax/swift,zisko/swift,JaSpa/swift,shahmishal/swift,arvedviehweger/swift,mightydeveloper/swift,hughbe/swift,cbrentharris/swift,tjw/swift,atrick/swift,swiftix/swift,ken0nek/swift,parkera/swift,return/swift,atrick/swift,adrfer/swift,benlangmuir/swift,frootloops/swift,emilstahl/swift,rudkx/swift,uasys/swift,russbishop/swift,MukeshKumarS/Swift,practicalswift/swift,austinzheng/swift,jmgc/swift,shahmishal/swift,hughbe/swift,manavgabhawala/swift,atrick/swift,sschiau/swift,stephentyrone/swift,ahoppen/swift,jopamer/swift,return/swift,xedin/swift,JGiola/swift,djwbrown/swift,sschiau/swift,danielmartin/swift,nathawes/swift,apple/swift,tjw/swift,LeoShimonaka/swift,return/swift,kstaring/swift,atrick/swift,ken0nek/swift,huonw/swift,swiftix/swift,parkera/swift,kusl/swift,brentdax/swift,huonw/swift,kusl/swift,stephentyrone/swift,adrfer/swift,devincoughlin/swift,nathawes/swift,gottesmm/swift,dduan/swift,roambotics/swift,emilstahl/swift,sdulal/swift,cbrentharris/swift,hughbe/swift,dduan/swift,SwiftAndroid/swift,KrishMunot/swift,sschiau/swift,xedin/swift,devincoughlin/swift,bitjammer/swift,swiftix/swift,amraboelela/swift,hooman/swift,huonw/swift,natecook1000/swift,atrick/swift,harlanhaskins/swift,Ivacker/swift,lorentey/swift,tinysun212/swift-windows,SwiftAndroid/swift,danielmartin/swift,KrishMunot/swift,tkremenek/swift,aschwaighofer/swift,apple/swift,xwu/swift,sdulal/swift,OscarSwanros/swift,mightydeveloper/swift,therealbnut/swift,russbishop/swift,tardieu/swift,tkremenek/swift,shajrawi/swift,sschiau/swift,stephentyrone/swift,CodaFi/swift,tinysun212/swift-windows,ben-ng/swift,stephentyrone/swift,milseman/swift,therealbnut/swift