[Metadata] Define _objc_empty_cache under SWIF_OBJC_INTEROP.
[Metadata] Define _objc_empty_cache under SWIF_OBJC_INTEROP.

Later code uses the variable under this macro, so defining it
under NDEBUG breaks debug builds of stdlib.

glessard/swift,airspeedswift/swift,tjw/swift,huonw/swift,nathawes/swift,airspeedswift/swift,allevato/swift,jopamer/swift,jmgc/swift,jmgc/swift,roambotics/swift,apple/swift,xwu/swift,hooman/swift,jckarter/swift,practicalswift/swift,jckarter/swift,glessard/swift,stephentyrone/swift,harlanhaskins/swift,CodaFi/swift,tkremenek/swift,tjw/swift,tjw/swift,jopamer/swift,practicalswift/swift,CodaFi/swift,shahmishal/swift,amraboelela/swift,amraboelela/swift,shahmishal/swift,karwa/swift,xedin/swift,CodaFi/swift,gribozavr/swift,lorentey/swift,shajrawi/swift,sschiau/swift,danielmartin/swift,apple/swift,benlangmuir/swift,benlangmuir/swift,shahmishal/swift,natecook1000/swift,hooman/swift,huonw/swift,hooman/swift,amraboelela/swift,tjw/swift,austinzheng/swift,nathawes/swift,jmgc/swift,natecook1000/swift,xedin/swift,gregomni/swift,lorentey/swift,ahoppen/swift,ahoppen/swift,apple/swift,xwu/swift,amraboelela/swift,shajrawi/swift,devincoughlin/swift,shajrawi/swift,allevato/swift,tkremenek/swift,jopamer/swift,amraboelela/swift,austinzheng/swift,practicalswift/swift,xedin/swift,karwa/swift,stephentyrone/swift,shahmishal/swift,gribozavr/swift,karwa/swift,karwa/swift,JGiola/swift,alblue/swift,apple/swift,atrick/swift,austinzheng/swift,tkremenek/swift,xwu/swift,gribozavr/swift,harlanhaskins/swift,nathawes/swift,jopamer/swift,rudkx/swift,atrick/swift,shahmishal/swift,ahoppen/swift,amraboelela/swift,nathawes/swift,austinzheng/swift,harlanhaskins/swift,alblue/swift,practicalswift/swift,apple/swift,danielmartin/swift,gribozavr/swift,brentdax/swift,roambotics/swift,xwu/swift,jmgc/swift,tkremenek/swift,xwu/swift,amraboelela/swift,parkera/swift,sschiau/swift,sschiau/swift,atrick/swift,shajrawi/swift,shahmishal/swift,sschiau/swift,hooman/swift,atrick/swift,parkera/swift,devincoughlin/swift,JGiola/swift,JGiola/swift,practicalswift/swift,ahoppen/swift,JGiola/swift,aschwaighofer/swift,gregomni/swift,aschwaighofer/swift,aschwaighofer/swift,lorentey/swift,gribozavr/swift,xedin/swift,tjw/swift,brentdax/swift,danielmartin/swift,stephentyrone/swift,nathawes/swift,jmgc/swift,tkremenek/swift,lorentey/swift,ahoppen/swift,airspeedswift/swift,danielmartin/swift,parkera/swift,brentdax/swift,roambotics/swift,huonw/swift,natecook1000/swift,tjw/swift,jopamer/swift,aschwaighofer/swift,devincoughlin/swift,practicalswift/swift,shajrawi/swift,practicalswift/swift,roambotics/swift,jckarter/swift,glessard/swift,tkremenek/swift,brentdax/swift,airspeedswift/swift,gregomni/swift,austinzheng/swift,atrick/swift,huonw/swift,sschiau/swift,lorentey/swift,gribozavr/swift,benlangmuir/swift,stephentyrone/swift,lorentey/swift,shajrawi/swift,airspeedswift/swift,austinzheng/swift,hooman/swift,allevato/swift,aschwaighofer/swift,glessard/swift,nathawes/swift,austinzheng/swift,gregomni/swift,CodaFi/swift,rudkx/swift,lorentey/swift,harlanhaskins/swift,shahmishal/swift,CodaFi/swift,karwa/swift,stephentyrone/swift,jopamer/swift,parkera/swift,jmgc/swift,benlangmuir/swift,xedin/swift,harlanhaskins/swift,huonw/swift,danielmartin/swift,sschiau/swift,tjw/swift,rudkx/swift,apple/swift,tkremenek/swift,hooman/swift,gribozavr/swift,jckarter/swift,allevato/swift,natecook1000/swift,brentdax/swift,nathawes/swift,alblue/swift,brentdax/swift,lorentey/swift,harlanhaskins/swift,roambotics/swift,huonw/swift,devincoughlin/swift,roambotics/swift,parkera/swift,allevato/swift,danielmartin/swift,alblue/swift,brentdax/swift,CodaFi/swift,harlanhaskins/swift,CodaFi/swift,ahoppen/swift,natecook1000/swift,karwa/swift,parkera/swift,aschwaighofer/swift,xedin/swift,xedin/swift,allevato/swift,natecook1000/swift,gribozavr/swift,glessard/swift,airspeedswift/swift,atrick/swift,benlangmuir/swift,danielmartin/swift,rudkx/swift,devincoughlin/swift,stephentyrone/swift,natecook1000/swift,devincoughlin/swift,airspeedswift/swift,shajrawi/swift,sschiau/swift,karwa/swift,gregomni/swift,shajrawi/swift,allevato/swift,JGiola/swift,huonw/swift,jckarter/swift,JGiola/swift,jckarter/swift,alblue/swift,rudkx/swift,alblue/swift,hooman/swift,gregomni/swift,stephentyrone/swift,alblue/swift,devincoughlin/swift,glessard/swift,jopamer/swift,rudkx/swift,practicalswift/swift,xedin/swift,jmgc/swift,parkera/swift,parkera/swift,xwu/swift,aschwaighofer/swift,devincoughlin/swift,karwa/swift,benlangmuir/swift,shahmishal/swift,sschiau/swift,jckarter/swift,xwu/swift