build: canonicalise the windows paths prior to use
build: canonicalise the windows paths prior to use

In order to substitute the path into the VFS overlay, we need to escape
the paths.  Instead, opt on the CMake behaviour of
`get_filename_component` providing the canonicalised path with forward
slashes rather than backslashes.  This allows the overlay to be used on
Windows as well as Linux.

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