[strliteral-upgrade] Change Strings.h constants to be constexpr static instead of static.
[strliteral-upgrade] Change Strings.h constants to be constexpr static instead of static.

Otherwise they can not be passed to StringLiteral. That would prevent me from
landing DaveZ's StringSwitch improvements from apple/swift-llvm#84 since
StringSwitch only takes StringLiterals now.

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