Replace getAs<> with dyn_cast<> on TypeVariableTypes.
Replace getAs<> with dyn_cast<> on TypeVariableTypes.

By construction, we can never have a type that desugars to a
TypeVariableType, so use dyn_cast<> rather than getAs<> for an easy 2%
speedup.


Swift SVN r3154

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