[CMake] Fix creation of swiftmodule directories on Apple platforms
[CMake] Fix creation of swiftmodule directories on Apple platforms

The way it was set up before worked for Ninja but not for Xcode, due
to me not listing the swiftmodule directories as actual outputs of the
create-directories target. The resulting fix here is actually simpler
and involves fewer processes anyway, so good for us.

https://bugs.swift.org/browse/SR-10029

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