[CMake] Simplify dependency generation for tests
[CMake] Simplify dependency generation for tests

SWIFT_NATIVE_SWIFT_TOOLS_PATH can be set to a path outside of the build
directory and the Xcode approach is simplier anyway.

nathawes/swift,nathawes/swift,hooman/swift,JGiola/swift,jckarter/swift,xwu/swift,allevato/swift,airspeedswift/swift,roambotics/swift,roambotics/swift,atrick/swift,hooman/swift,parkera/swift,nathawes/swift,airspeedswift/swift,tkremenek/swift,jmgc/swift,benlangmuir/swift,glessard/swift,gregomni/swift,gregomni/swift,apple/swift,benlangmuir/swift,nathawes/swift,apple/swift,hooman/swift,JGiola/swift,airspeedswift/swift,benlangmuir/swift,parkera/swift,atrick/swift,airspeedswift/swift,allevato/swift,parkera/swift,JGiola/swift,JGiola/swift,glessard/swift,parkera/swift,CodaFi/swift,roambotics/swift,parkera/swift,hooman/swift,glessard/swift,apple/swift,CodaFi/swift,hooman/swift,airspeedswift/swift,atrick/swift,rudkx/swift,airspeedswift/swift,CodaFi/swift,apple/swift,airspeedswift/swift,jmgc/swift,ahoppen/swift,tkremenek/swift,parkera/swift,jmgc/swift,jckarter/swift,JGiola/swift,allevato/swift,nathawes/swift,apple/swift,hooman/swift,gregomni/swift,rudkx/swift,CodaFi/swift,allevato/swift,allevato/swift,jmgc/swift,CodaFi/swift,tkremenek/swift,gregomni/swift,gregomni/swift,tkremenek/swift,ahoppen/swift,xwu/swift,glessard/swift,benlangmuir/swift,rudkx/swift,xwu/swift,jmgc/swift,roambotics/swift,parkera/swift,benlangmuir/swift,atrick/swift,rudkx/swift,tkremenek/swift,JGiola/swift,jmgc/swift,rudkx/swift,xwu/swift,ahoppen/swift,parkera/swift,jckarter/swift,ahoppen/swift,jckarter/swift,xwu/swift,atrick/swift,tkremenek/swift,atrick/swift,allevato/swift,allevato/swift,benlangmuir/swift,jckarter/swift,nathawes/swift,xwu/swift,ahoppen/swift,roambotics/swift,gregomni/swift,xwu/swift,glessard/swift,jmgc/swift,jckarter/swift,rudkx/swift,CodaFi/swift,tkremenek/swift,nathawes/swift,CodaFi/swift,roambotics/swift,ahoppen/swift,glessard/swift,hooman/swift,apple/swift,jckarter/swift