[stdlib] Speculative workaround for ASAN failure
[stdlib] Speculative workaround for ASAN failure

I suspect the fancy _unsafeUpcast implementation, that was supposed to
be more optimizable, was confusing the optimizer, and that is the cause
of ASAN failures we're seeing.  Let's see if this makes ASAN happy
again.

parkera/swift,gregomni/swift,manavgabhawala/swift,deyton/swift,kstaring/swift,jtbandes/swift,gmilos/swift,practicalswift/swift,zisko/swift,lorentey/swift,ben-ng/swift,frootloops/swift,zisko/swift,natecook1000/swift,jckarter/swift,xwu/swift,gmilos/swift,gottesmm/swift,amraboelela/swift,JaSpa/swift,IngmarStein/swift,swiftix/swift,brentdax/swift,brentdax/swift,bitjammer/swift,harlanhaskins/swift,gregomni/swift,therealbnut/swift,CodaFi/swift,tkremenek/swift,tinysun212/swift-windows,CodaFi/swift,stephentyrone/swift,shajrawi/swift,allevato/swift,shajrawi/swift,kperryua/swift,allevato/swift,practicalswift/swift,manavgabhawala/swift,jckarter/swift,shahmishal/swift,sschiau/swift,return/swift,parkera/swift,CodaFi/swift,glessard/swift,benlangmuir/swift,gottesmm/swift,ahoppen/swift,gmilos/swift,kstaring/swift,austinzheng/swift,atrick/swift,atrick/swift,felix91gr/swift,therealbnut/swift,huonw/swift,frootloops/swift,tkremenek/swift,OscarSwanros/swift,atrick/swift,karwa/swift,harlanhaskins/swift,danielmartin/swift,apple/swift,ahoppen/swift,modocache/swift,danielmartin/swift,danielmartin/swift,devincoughlin/swift,roambotics/swift,OscarSwanros/swift,calebd/swift,benlangmuir/swift,gribozavr/swift,hughbe/swift,gregomni/swift,shahmishal/swift,therealbnut/swift,IngmarStein/swift,harlanhaskins/swift,djwbrown/swift,JaSpa/swift,practicalswift/swift,sschiau/swift,therealbnut/swift,ahoppen/swift,hooman/swift,felix91gr/swift,brentdax/swift,kperryua/swift,benlangmuir/swift,natecook1000/swift,milseman/swift,tinysun212/swift-windows,IngmarStein/swift,austinzheng/swift,devincoughlin/swift,austinzheng/swift,airspeedswift/swift,IngmarStein/swift,Jnosh/swift,frootloops/swift,xwu/swift,lorentey/swift,xedin/swift,ben-ng/swift,sschiau/swift,JGiola/swift,gribozavr/swift,nathawes/swift,sschiau/swift,tkremenek/swift,modocache/swift,lorentey/swift,kperryua/swift,shahmishal/swift,xwu/swift,roambotics/swift,IngmarStein/swift,jtbandes/swift,Jnosh/swift,tinysun212/swift-windows,return/swift,OscarSwanros/swift,felix91gr/swift,practicalswift/swift,apple/swift,aschwaighofer/swift,deyton/swift,hughbe/swift,stephentyrone/swift,hooman/swift,gmilos/swift,shajrawi/swift,apple/swift,swiftix/swift,practicalswift/swift,amraboelela/swift,natecook1000/swift,aschwaighofer/swift,uasys/swift,djwbrown/swift,zisko/swift,return/swift,tjw/swift,sschiau/swift,deyton/swift,gottesmm/swift,bitjammer/swift,tardieu/swift,shahmishal/swift,JGiola/swift,xedin/swift,OscarSwanros/swift,gregomni/swift,devincoughlin/swift,xwu/swift,kperryua/swift,JGiola/swift,gottesmm/swift,nathawes/swift,JaSpa/swift,milseman/swift,hughbe/swift,kstaring/swift,tardieu/swift,shajrawi/swift,benlangmuir/swift,milseman/swift,therealbnut/swift,jopamer/swift,karwa/swift,aschwaighofer/swift,manavgabhawala/swift,bitjammer/swift,ahoppen/swift,natecook1000/swift,ben-ng/swift,alblue/swift,deyton/swift,karwa/swift,tardieu/swift,devincoughlin/swift,airspeedswift/swift,return/swift,tjw/swift,glessard/swift,austinzheng/swift,kstaring/swift,IngmarStein/swift,OscarSwanros/swift,jopamer/swift,jmgc/swift,frootloops/swift,frootloops/swift,apple/swift,IngmarStein/swift,arvedviehweger/swift,manavgabhawala/swift,arvedviehweger/swift,codestergit/swift,austinzheng/swift,alblue/swift,CodaFi/swift,tkremenek/swift,sschiau/swift,milseman/swift,stephentyrone/swift,karwa/swift,tjw/swift,hughbe/swift,jtbandes/swift,stephentyrone/swift,lorentey/swift,devincoughlin/swift,karwa/swift,djwbrown/swift,codestergit/swift,alblue/swift,arvedviehweger/swift,aschwaighofer/swift,Jnosh/swift,karwa/swift,milseman/swift,tardieu/swift,devincoughlin/swift,stephentyrone/swift,jckarter/swift,shajrawi/swift,bitjammer/swift,uasys/swift,gribozavr/swift,atrick/swift,rudkx/swift,gribozavr/swift,gottesmm/swift,glessard/swift,codestergit/swift,ben-ng/swift,brentdax/swift,CodaFi/swift,shajrawi/swift,danielmartin/swift,JGiola/swift,jckarter/swift,ahoppen/swift,calebd/swift,jmgc/swift,xedin/swift,amraboelela/swift,nathawes/swift,gribozavr/swift,karwa/swift,manavgabhawala/swift,alblue/swift,hughbe/swift,glessard/swift,arvedviehweger/swift,apple/swift,harlanhaskins/swift,xwu/swift,ben-ng/swift,sschiau/swift,natecook1000/swift,milseman/swift,amraboelela/swift,practicalswift/swift,practicalswift/swift,swiftix/swift,parkera/swift,jtbandes/swift,huonw/swift,benlangmuir/swift,modocache/swift,huonw/swift,Jnosh/swift,stephentyrone/swift,allevato/swift,Jnosh/swift,return/swift,jckarter/swift,JaSpa/swift,jmgc/swift,amraboelela/swift,gribozavr/swift,allevato/swift,modocache/swift,kstaring/swift,modocache/swift,aschwaighofer/swift,rudkx/swift,devincoughlin/swift,nathawes/swift,felix91gr/swift,codestergit/swift,apple/swift,gregomni/swift,airspeedswift/swift,atrick/swift,glessard/swift,harlanhaskins/swift,huonw/swift,shajrawi/swift,shajrawi/swift,kperryua/swift,natecook1000/swift,Jnosh/swift,xwu/swift,OscarSwanros/swift,ben-ng/swift,djwbrown/swift,manavgabhawala/swift,allevato/swift,jmgc/swift,natecook1000/swift,nathawes/swift,uasys/swift,tardieu/swift,calebd/swift,rudkx/swift,tinysun212/swift-windows,tjw/swift,airspeedswift/swift,CodaFi/swift,shahmishal/swift,gmilos/swift,xedin/swift,OscarSwanros/swift,zisko/swift,JaSpa/swift,tinysun212/swift-windows,parkera/swift,arvedviehweger/swift,kstaring/swift,Jnosh/swift,deyton/swift,ahoppen/swift,djwbrown/swift,jmgc/swift,alblue/swift,gregomni/swift,danielmartin/swift,tjw/swift,jmgc/swift,modocache/swift,JaSpa/swift,djwbrown/swift,tinysun212/swift-windows,parkera/swift,calebd/swift,JGiola/swift,alblue/swift,deyton/swift,kstaring/swift,calebd/swift,jtbandes/swift,hughbe/swift,roambotics/swift,arvedviehweger/swift,uasys/swift,shahmishal/swift,kperryua/swift,parkera/swift,tkremenek/swift,allevato/swift,zisko/swift,airspeedswift/swift,hooman/swift,amraboelela/swift,uasys/swift,return/swift,felix91gr/swift,huonw/swift,airspeedswift/swift,modocache/swift,jckarter/swift,tkremenek/swift,huonw/swift,calebd/swift,parkera/swift,nathawes/swift,brentdax/swift,swiftix/swift,JaSpa/swift,hooman/swift,return/swift,lorentey/swift,austinzheng/swift,rudkx/swift,alblue/swift,hooman/swift,swiftix/swift,hooman/swift,parkera/swift,xedin/swift,bitjammer/swift,jmgc/swift,glessard/swift,danielmartin/swift,milseman/swift,uasys/swift,tardieu/swift,gottesmm/swift,roambotics/swift,roambotics/swift,hughbe/swift,zisko/swift,bitjammer/swift,shahmishal/swift,arvedviehweger/swift,danielmartin/swift,lorentey/swift,stephentyrone/swift,xedin/swift,aschwaighofer/swift,xedin/swift,swiftix/swift,tjw/swift,nathawes/swift,ben-ng/swift,brentdax/swift,roambotics/swift,felix91gr/swift,gmilos/swift,allevato/swift,karwa/swift,zisko/swift,huonw/swift,xedin/swift,tinysun212/swift-windows,therealbnut/swift,benlangmuir/swift,tardieu/swift,shahmishal/swift,CodaFi/swift,codestergit/swift,jopamer/swift,brentdax/swift,hooman/swift,airspeedswift/swift,jtbandes/swift,frootloops/swift,practicalswift/swift,swiftix/swift,rudkx/swift,gmilos/swift,manavgabhawala/swift,tjw/swift,jckarter/swift,austinzheng/swift,lorentey/swift,frootloops/swift,JGiola/swift,harlanhaskins/swift,jopamer/swift,gottesmm/swift,deyton/swift,aschwaighofer/swift,uasys/swift,calebd/swift,felix91gr/swift,codestergit/swift,lorentey/swift,jopamer/swift,gribozavr/swift,harlanhaskins/swift,amraboelela/swift,djwbrown/swift,jopamer/swift,kperryua/swift,therealbnut/swift,codestergit/swift,gribozavr/swift,bitjammer/swift,sschiau/swift,jtbandes/swift,tkremenek/swift,jopamer/swift,atrick/swift,xwu/swift,rudkx/swift,devincoughlin/swift