[CMake] Quote use of SWIFT_PATH_TO_LIBDISPATCH_SOURCE
[CMake] Quote use of SWIFT_PATH_TO_LIBDISPATCH_SOURCE

If the variable is empty, expanding it without quoting can end up with
invalid CMake syntax. We get away with it here because of how the if
happens to be structured, but adding an OR clause after the EXISTS
clause would expose the issue, for example.

shahmishal/swift,roambotics/swift,glessard/swift,CodaFi/swift,devincoughlin/swift,jmgc/swift,gribozavr/swift,airspeedswift/swift,nathawes/swift,shahmishal/swift,benlangmuir/swift,ahoppen/swift,xwu/swift,gregomni/swift,devincoughlin/swift,aschwaighofer/swift,JGiola/swift,ahoppen/swift,jckarter/swift,karwa/swift,karwa/swift,xwu/swift,gregomni/swift,rudkx/swift,gribozavr/swift,nathawes/swift,stephentyrone/swift,airspeedswift/swift,roambotics/swift,atrick/swift,CodaFi/swift,gribozavr/swift,jmgc/swift,devincoughlin/swift,allevato/swift,atrick/swift,parkera/swift,airspeedswift/swift,hooman/swift,rudkx/swift,aschwaighofer/swift,JGiola/swift,stephentyrone/swift,shahmishal/swift,tkremenek/swift,xwu/swift,apple/swift,gribozavr/swift,sschiau/swift,xwu/swift,benlangmuir/swift,airspeedswift/swift,apple/swift,lorentey/swift,CodaFi/swift,hooman/swift,parkera/swift,nathawes/swift,jmgc/swift,CodaFi/swift,tkremenek/swift,hooman/swift,atrick/swift,nathawes/swift,ahoppen/swift,JGiola/swift,jmgc/swift,rudkx/swift,karwa/swift,allevato/swift,jckarter/swift,jckarter/swift,gregomni/swift,jmgc/swift,glessard/swift,devincoughlin/swift,apple/swift,apple/swift,airspeedswift/swift,jckarter/swift,rudkx/swift,rudkx/swift,nathawes/swift,gregomni/swift,gribozavr/swift,apple/swift,lorentey/swift,benlangmuir/swift,devincoughlin/swift,aschwaighofer/swift,aschwaighofer/swift,allevato/swift,atrick/swift,xwu/swift,devincoughlin/swift,shahmishal/swift,karwa/swift,karwa/swift,harlanhaskins/swift,airspeedswift/swift,aschwaighofer/swift,karwa/swift,harlanhaskins/swift,devincoughlin/swift,harlanhaskins/swift,ahoppen/swift,glessard/swift,JGiola/swift,airspeedswift/swift,parkera/swift,sschiau/swift,lorentey/swift,rudkx/swift,harlanhaskins/swift,atrick/swift,karwa/swift,stephentyrone/swift,aschwaighofer/swift,jmgc/swift,gregomni/swift,roambotics/swift,ahoppen/swift,allevato/swift,gregomni/swift,hooman/swift,shahmishal/swift,gribozavr/swift,sschiau/swift,stephentyrone/swift,stephentyrone/swift,nathawes/swift,xwu/swift,karwa/swift,lorentey/swift,parkera/swift,allevato/swift,shahmishal/swift,tkremenek/swift,allevato/swift,devincoughlin/swift,benlangmuir/swift,stephentyrone/swift,roambotics/swift,glessard/swift,lorentey/swift,harlanhaskins/swift,JGiola/swift,benlangmuir/swift,CodaFi/swift,parkera/swift,lorentey/swift,hooman/swift,sschiau/swift,tkremenek/swift,parkera/swift,jckarter/swift,parkera/swift,sschiau/swift,CodaFi/swift,tkremenek/swift,tkremenek/swift,harlanhaskins/swift,gribozavr/swift,harlanhaskins/swift,shahmishal/swift,CodaFi/swift,roambotics/swift,lorentey/swift,atrick/swift,tkremenek/swift,lorentey/swift,hooman/swift,ahoppen/swift,shahmishal/swift,nathawes/swift,JGiola/swift,jckarter/swift,glessard/swift,apple/swift,sschiau/swift,roambotics/swift,sschiau/swift,stephentyrone/swift,allevato/swift,benlangmuir/swift,jckarter/swift,xwu/swift,aschwaighofer/swift,glessard/swift,jmgc/swift,sschiau/swift,gribozavr/swift,parkera/swift,hooman/swift