[stdlib] Factor out _fixLifetime
[stdlib] Factor out _fixLifetime

Apparently Builtin.fixLifetime isn't yet respected
(<rdar://problem/16464507>) and calls to that and swift_keepAlive were
getting scattered around randomly.  Let's have a convenient library
function instead.

Swift SVN r17493

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